Category Archives: The Crime Scene
Stringing Bloodstains: The Old School Method
Today I’ve been invited to share a post at Writing With the Top Down BLOG on this method of determining the three dimensional area of origin in bloodstain pattern analysis. I’d love it if you could stop by and take a look.
Introducing the M-Vac DNA Vacuum
I love introducing you to cutting edge technologies that may turn your reader’s heads and make them turn the page. Forensics has never been a stagnant science. Dozens of researchers are pushing envelopes and making the imaginable come to fruition. One such device is the M-Vac. This recent addition to the CSI tool kit may revolutionize how we search for evidence and recover DNA that was previously unrecoverable. Vacuums are nothing new to the collection of trace evidence. I need to write a post on the history of the trace evidence vacuum which was introduced at early as the 1930′s. The M-Vac is the next generation trace evidence vacuum designed specifically for DNA collection.
Forensic scientists have made great progress in the collection, analysis, and turn around time of DNA testing in the last decade. The M-Vac uses a wet-vacuum method to release stubborn cells from evidence like clothing, textured pistol grips, and other surfaces where the samples may be hard to get at with swabs. It uses a DNA-free buffer solution that is applied and then recovered in one step through the application wand. The solution carrying the DNA samples is then deposited in a sterile collection bottle that can be tested for DNA profiles. The wand allows the CSIs to cover large areas and get into nooks and crannies that prove too difficult for swabs. Validation studies have indicated that the M-Vac collects 39 times more DNA than swabbing!
I’ve included a short video below that demonstrates some collection methods. One sampling procedure that wasn’t covered was the autopsy. I’m not sure what possible roadblocks may exist (if any) but it seems to me that this sampling method may prove very valuable in sampling certain areas of the victim’s body. Imagine sampling the neck in a strangulation case, genitals or breasts in a sexual assault, the wrists or ankles in a body dump where the victim was dragged, or even the victim’s hair. You may also get results from the outsole of a shoe used in a stomping or the hood of a vehicle in a hit and run. As the video indicates, this tech may open up new leads in cold cases as well. The possibilities are pretty endless it seems.
If your next novel deals with DNA evidence you might consider using a device like this. I suspect there are a number of CSIs and detectives who may be unaware of this technology. Imagine their surprise at reading about it in your novel.
What the Heck is Entomotoxicology?
The House fly
I’ve written before about the role of the forensic entomologist in death investigations. These professionals can provide critical information regarding the time since colonization and postmortem processes. One aspect of their analysis that is being utilized for frequently is the use of insects (like maggots) to screen for the presence of drugs or toxins (like Malathion). Before I get into the process, let’s discuss why this type of testing might be undertaken. Obviously, the presence of illicit drugs like cocaine, heroine, MDMA, or amphetamines, may provide critical information about a possible cause of death, criminal activity, and victimology. In the same light, the presence of prescription drugs may also shed light on the victim and their physical or mental health. Likewise, the absence of certain drugs may also reveal important clues surrounding the victim’s state of health. Did they need the medication to maintain a certain quality of life or health status?
Why not just review their medical records? First, the victim may not have a complete documented medical history. Some people gain access to prescription drugs through illegal or unethical means. Family members (even spouses or parents) may be unaware of certain health conditions. Additionally, the victim may not be identified at the crime scene. Insects like maggots can removes significant biomass during the decomposition process and some victim’s don’t have any identification on them. We may be able to extract DNA but that will be of little help if their profile is not on file. We may be able to construct certain features or details about their lives based on their physical possessions (clothing size, piercings, tattoos, etc.) but the presence of certain drugs or toxins may provide that extra clue that helps to narrow down missing person profiles.
The concept of using insects for drug screening is pretty straight forward. While the victim’s tissues and fluids (blood, urine) degrade through decomposition; the larvae do not. In effect, they act as mini-reservoirs. Eventually they will undergo some kind of metamorphosis but if they are found on a body they can be tested. As adults they tend to eliminate the toxins rather quickly but even trace amounts of some drugs have been found in recently emerged adult flies. Some research has even detected drugs in beetle frass (excrement) and fly puparia years after death. Testing is begun by crushing or grinding the insect samples in something like a mortar and pestle. There are a number of different tests that can then be performed including Gas Chromatography / Mass Spectrometry (GC/MS), Fourier Transform Infrared Spectroscopy (FTIR), and radioimmunoassay (RIA). In many ways the testing sample is treated like any other biological tissue. The effects of various drugs and toxins on the rate of biological development (of the larvae) is not fully known. These types of exams primarily screen for the presence or absence of drugs and toxins. The effects of such substances on insect biology is another matter the entomologist must consider when estimating the postmortem interval.
As authors you may consider using insects as a testing source for drugs or toxins, especially when other tissues are not viable. Consider too the absence of certain prescribed drugs that may affect the victim’s behavior or general health. The drugs may be illegal or they may have been stolen by the suspect from another family member, friend, or co-worker. The presence or absence of drugs or toxins may also reveal a “unique” data point in the unidentified victim’s profile to compare against missing person’s records, medical records, or even criminal modus operandi (such as the use of a date rape drug or poisoning by mercury). You probably already have an interesting application of drugs or toxins in your storyline. The use of insects to test for those substances will provide for some interesting dialog between characters or plot twists for your readers.
Hidden Paths to Hidden Worlds
I love being out in the woods. I don’t mind walking established trails but it takes no convincing to get me “off trail”. One of the reasons I love getting off the beaten path is that I get to see things most people don’t. Wild critters, small brooks, or hidden canyons. I sit and wonder how long it has been since another person was seeing what I’m seeing.Most of the time I’m not that far away from the rest of those enjoying the outdoors. Maybe just over a hill or around a bend but, it makes all the difference in the experience. I often think “wow”, I would have never seen that bear, bobcat, or elk if I hadn’t come this way.
In the modern world we’re conditioned to follow certain paths. Sidewalks, roads, green belts, subways, etc. Think about it…don’t you take the same path to work everyday? What about the grocerie store, gas station, or your child’s school? Partly this is because we’ve determined the easiest, most efficient, route. But even when you’re going somewhere new you generally stay on some kind of path right? Don’t most of you hesitate to cross open space unless there is a trail? Even then, if there is a sign prohibiting it, most people won’t. This type of thinking limits the world we see and experience. Criminals aren’t restrained by thinking.
One of the toughest things to learn as a new CSI is to stop thinking like everyone else and start thinking like a criminal. You have to divorce yourself from even the most basic and accepted thoughts. Criminals have to conduct their “business” and get from point A to point B but, some of them don’t want to draw attention to themselves (just like animals). At least the successful ones don’t. They like to conduct their business in the “shadows” or “off the beaten path”. There is a whole world of activity going on right now…off that beaten path. These are worlds within worlds and it is the job of the CSI to find them (at least as they pertain to criminal activity).
These are places where most of us have no reason to go. Culverts, abandoned buildings, tunnels, and over grown gulches. Sometimes these places are right under our noses. I remember being a young officer and getting a call about a “satanic” alter being found at a movie theater. Turns out there was a “hidden” room above the concession stand but below the projector room. In the old days they used the room to cut film reels. It hadn’t been used in decades for that reason but someone was using it now. There was no way to tell how long it had been in use but that’s not my point. The point is that the activities were going on right under everyone’s noses because no one ever had reason to go in there. The room was “off limits”.
Don’t forget about these “hidden worlds” in your writing. I’ve made it a point in my novels to include such places and I think it adds a powerful layer of mystery to the settings. These places are even more frightening when your characters stumble upon them for the first time. It may be a detective, teenage runaway, or concerned parent. The possibilities are endless and can be driven by the structure itself. The video below is apparently from an old missile silo. Imagine the types of crimes that could be going on in such a place and how hard it would be for someone to stumble upon it? Might be a good idea for a novel eh?
Interview with Forensic Geologist Jim Reed
I have a special treat for you today F4F readers. Jim Reed is currently the Director of Research & Development for RockWare Incorporated, a geological software company based in Golden, Colorado with a European office in Lugano, Switzerland. Jim began studying geology at the University of Wyoming and ended up at Washington University in St. Louis, Missouri. His career as a geologist began in 1973 when he worked for NASA on the Mars Viking Lander project while moonlighting for Arch Minerals computing coal reserves in the Illinois Basin. He then went on to work as a project-level field geologist for Freeport Exploration (copper, gold, silver) in the Mojave Desert and southern New Mexico. From there, he became a regional-level field geologist for AMAX Exploration (molybdenum) in the Sierra Nevada of Northern California and the Trans-Pecos regions of southwestern Texas. He then became a senior geologist at Wold Minerals (uranium & talc) based in Austin, Texas. Since founding RockWare in 1983, Jim has worked in China, Africa, Cyprus, Russia and Papua New Guinea. His expertise includes environmental site contamination characterization, hydrogeology, mining, petroleum, and geotechnical volumetrics (computing the shape and mass of buried objects). I have known and worked with Jim for a number of years in NecroSearch and he’s the real deal.
F4F: Tell us a little about how you first became involved in forensic investigations?
REED: About 20 years ago, I got a call from Clark Davenport, a crazy geophysicist and soon-to-be mentor and lifelong friend, who was one of the co-founders of NecroSearch, a newly-formed, non-profit organization made up of volunteers from a variety of disciplines, many of which I had never even heard of. Entomology? What’s that? They were looking for a geo-nerd to apply geological software to their investigations. The timing was perfect because I was looking for something civic to become involved in. So I showed up at their next meeting and was absolutely captivated by the idea of working with real cops on real crimes. As a kid, I was always in trouble with the cops, so this was my chance to flip things around. Personal computing was fairly new at the time so I was considered a god. Nowadays, everybody in the group just thinks of me as an obnoxious computer geek.
F4F: Can you tell the readers the difference between forensic geology and geophysics?
REED: Geophysicists are just geologists who could pass calculus and physics. Geophysics always involves complicated-looking electronic gizmos with lots of blinking lights that measure things like soil conductivity (e.g. moisture) using outrageously simple concepts that are disguised by fancy jargon. I’m not exaggerating. Really. Consider a “resistivity” survey. Connect a wire from the positive end of a battery to a voltmeter. Then run a wire from the other pole of the voltmeter and stick it into the ground. Run a wire from the negative side of the battery into the ground, and voila, you’ve got a “resistivity meter” or a “soil conductivity meter”. By comparison, geologists are typically limited to rock hammers, colored pencils, and a compass, albeit a fancy compass. The term “forensics” has been muddied over the years to essentially apply to any endeavor that involves lawyers. If somebody’s house slips off its foundation, the homeowner’s attorney may hire a “forensic engineering geologist” to testify in the lawsuit with the contractor. The forensic engineering geologist, as opposed to a plain ol’ engineering geologist, knows to look at the jury and the judge when he/she answers a question rather than looking at the person who asked the question. That’s about it. In regards to crime-fighting, I consider a “forensic” prefix to mean that you know how to conduct yourself at a crime scene (drinking coffee, eating donuts, and swapping jokes), collect evidence, and provide expert testimony at the trial.
F4F: Most, if not all, forensic geologists are employed by private industry or universities. What do you see as the biggest challenge for a geologist working a forensic case for the first time?
REED: Wow, “for the first time”? That’s tough. I think the biggest challenge is to act like you know what you’re doing. Seriously. You may be at the top of your game geology-wise, but I can guarantee that you’ll fall apart on your first case. Here’s why; methodical, well-planned field methods fall apart when Channel X turns on the bright lights, sticks a microphone in your face, and the cutie asks a question that is so outrageously stupid that your brain locks up in an infinite loop, unable to come up with an answer that doesn’t come off as smartass, condescending, or extremely nerdy. In the end, you just come off as an idiot. Most geologists are used to working in remote locations by themselves where there’s nobody to see you screw up the first three times. It doesn’t help when you overhear law enforcement guys laughing amongst themselves, saying “Damn, I could have dug up this site with a backhoe in the time that it’s taking that geo-guy to figure out his GPS.” My advice to a geologist who’s working their first case is to find a mentor and mimic their every move. Another problem is that most science curricula beat young students over the head with the concept of the “observer effect” which essentially states that you can’t measure anything without effecting the outcome of the experiment. On a crime scene, the geologist becomes overwhelmed with this principle. How can I measure soil compaction if all of these crimes scene technicians are stomping all over the place?
F4F: What are some of the most effective technologies in remote sensing for law enforcement in your opinion?
REED: Oh boy, how much space do I have to answer this one? Well, let’s start with the least “invasive”, meaning techniques that don’t screw up the crime scene. First off, there’s conventional satellite imagery. Google Earth is the starting point, especially if you use their historical imagery capability to compare images before and after the date when the evidence was buried. Next comes higher-resolution imagery, typically from the local tax assessor or the utility companies. An infrared camera is a great tool because you can look for ground that has a weird thermal “signature”. I don’t mean ground that’s glowing with heat because a body is decomposing, but rather subtle differences related to how the disturbed soil is heating up or cooling off during a 24-hour period. From here, we start in with the geophysics, measuring things such as soil moisture because anybody who’s ever planted a garden knows that turning the soil increases its ability to hold moisture. Then comes ground penetrating radar (GPR) in which we’re looking for disturbances within the natural layering of the soil layers. If there’s reason to believe that ferrous metals (anything that can rust) are buried along with the victim, we might use a magnetometer which measures the magnetic field produced by elements such as iron. An invasive gizmo called a “cone penetrometer” can be used to measure the compaction of the soil. This is essentially a very expensive metal rod that you push into the ground. The penetrometer measures the pressure required to push the rod point to various depth levels. Once you start in with these types of “geo-technical” tools, you’re disturbing the site, so it’s import to start with the least invasive methods and then progress towards the destructive. Sort of like medicine. Start by asking about the symptoms, suggest some changes to diet, exercise, etc. before you pull out the scalpel.
F4F: I can’t think of anyone that has used technology more effectively to advance our abilities to locate clandestine graves. Can you talk about how you’ve adapted RockWare technology to forensic science?
REED: Thanks. I’m blushing. Mostly, I’ve added a bunch of programs to RockWorks for merging the data from the different disciplines and boiling it down to a single target. This means “normalizing” the data from the botanists, the remote sensing (e.g. thermal), geophysics, etc. so that we can compare apples with apples. The next step is to “standardize” these spatial (map) data sets such that they’re expressed in terms of “standard deviations from the mean”. That’s a fancy way of saying that we’re converting the data to units that represent weirdness relative to undisturbed terrain. Finally, these programs boil all of this disparate information into a “dig here” map. The technical terminology for this type of analysis is “N-dimensional, multi-variant, weighted spatial analysis” – a great term to throw out when you want to intimidate a cross-examining defense attorney. Another big improvement, thanks to the on-site forensic experience involves ease-of-use. It’s one thing to write a program that you can use if you’re sitting in a quiet office with the luxury of silence and a user manual. It’s another thing to create an interface that is useable on the hood of a squad car when everybody around you is making you nervous. We’ve also added one-click export to Google Earth thereby eliminating the coordinate conversion hassles that drive investigators away from computers.
F4F: You worked on high profile cases all over the world. What was your most memorable experience?
REED: There have certainly been some cases that impress my friends, like going to Russia to look for Anastasia Romanov, but the ones that I remember the best are the ones that I’d really like to forget. Don’t get me wrong; the rewards from this type of work are profound. Directly helping to put the boogie-man away, providing “closure” to family members, working with world-class scientists, befriending some of the greatest law enforcement people – these are the some of the many benefits. But … in the last few years I’ve been paired up to work side-by-side, in the field, with cooperative perpetrators including serial murderers. Being nonchalant and friendly with these guys has taken a toll. In one instance, I left the group for about a year until the nightmares went away. Eventually, I realized that there was a hole in my life that NecroSearch filled so I became active again and sure enough the nightmares started right back up. The difference is that I now accept them as “normal” costs well worth the benefits. Part of the job.
F4F: You’re on the forefront of new technology. What do you see emerging in the next five or ten years that may help law enforcement find clandestine graves?
REED: Ground-based LIDaR (Laser Imaging Detection and Ranging) is going to absolutely and unequivocally revolutionize crime scene investigations. Most law enforcement folks haven’t even heard of it yet, but trust me, it will change everything. Here’s how it works; You arrive at the scene, set up a tripod, mount a clunky gizmo on top, turn it on, and walk away. The LIDaR laser/camera sweeps up and down while rotating, recording the location and color of everything at the site. Every blade of grass. Every twig. Everything. You pull out the memory card, plug it into a laptop and you’ve got a color “point cloud” that exactly reproduces the crime scene in three dimensions. Right now, LIDaR is incredibly expensive, but so was GPS twenty years ago and now every cop has one. For NecroSearch, I see LIDaR allowing us to create micro-topographic surfaces that will show the slightest disturbance (e.g. subsidence). Anybody who has ever visited an old graveyard knows what happens to the ground surface over time. You don’t even need to bury something to create a topographic “anomaly” – just dig a hole, backfill it, and return in a year. You may now be able to see it, but LIDaR will.
For more information about RockWare and their flagship product, RockWorks, visit: www.rockware.com
MacGuyver Forensics: Carbon Paper Shoe Lifts
Papers on the floor in a crime scene
Real life CSIs sometimes have to find innovative ways to capture evidence. There are a ton of commercial products available for nearly every type of evidence but Murphy has a tendency to rear his ugly head at the most inopportune times (like a homicide scene). Cameras break, your partner forgot to re-stock supplies, or you simply run out. In most cases you can’t just run down to the local Walmart and pick up exactly what you need. Good CSIs learn to develop alternative methods of collecting and preserving evidence (if possible) in the event you need to have a fall back plan. Some purists may scoff at such an idea but in my opinion it’s better to have something collected than nothing collected. The need to use unconventional collection methods is probably more likely for your private detective or amateur detective character. These folks may not have an impressive array of CSI gear because they don’t have to concern themselves with those matters often.
I’ve noted before that footwear evidence is one of the most commonly overlooked categories of physical evidence at a crime scene. Some of that is due to a lack of training, lack of awareness, or simply not having the proper equipment. In real life, the crime lab isn’t called to every crime scene. Usually we just go to the major scenes. Patrol officers don’t carry around electro-static dust print lifters, alternate light sources, and other specialized equipment so sometimes footwear evidence gets overlooked. One of the better surfaces to find two dimensional footwear impressions at crime scenes is paper. Paper may get scattered on the floor during a ransacking or it may just be trash on the floor (like in a warehouse). You can even find these dust prints on broken drywall, carpeting, or doors that have been kicked. Either way it can hold valuable clues. These impressions can be latent (invisible) and need some degree of processing to make visible again.
So what is your amateur detective to do when he/she spots a sheet of paper at the crime scene and thinks there’s a footwear impression on it? One simple process is to use blue carbon paper to make a lift. For some reason, black carbon paper isn’t as good. The process is really quite easy. You start by taking the paper evidence and securing it to a hard flat surface. Taping the corners works well. Then you lay a sheet of blue carbon paper down over the area you think may hold the dust print. Cover that carbon sheet with a manilla file folder or pad of paper and use a 4″ rubber roller to “press” the dust print onto the blue carbon paper. Simply roll the rubber roller firmly back and forth over the area a few times to transfer the image.
Carbon paper over print on newspaper
Using a roller to transfer the impression to the carbon paper
Once that is done the detective can flip over the carbon paper and use a strong oblique light (like a flashlight) to see the image in a darkened room. Any windowless room (like a powder room) works well. Voila! The invisible shoe print is now visible. It may be possible to individualize an impression to a particular shoe but even knowing the make and model of the shoe can be helpful in an investigation. If your prime suspect only wears Nike and the shoe in question is a cowboy boot you may need to search for another suspect right? In the end, a professional CSI would probably get better results using a gel lifter or ESDL but keep this trick in mind when writing your scenes. If your “detective” is unprepared then this might be a good option to recover evidence others may have missed.
Back Spatter from Gunshot Injuries
Back spatter can also travel down the barrel!
There are basically two types of blood spatter; forward and back. Notice I didn’t say “splatter“. Blood spatter is caused when an object impacts a body and forces the blood to break up into smaller droplets. The majority of these droplets are then projected either forward (with direction of force) or backward (opposite the direction of force) essentially. Generally speaking, there is more forward spatter than back spatter in an incident and the blood will disperse in a “cone effect”. The amount of back spatter is dependent on both the energy of the impact and the amount of blood already present at the impact site. For example, a gunshot can create back spatter even when there is no preceding injury. This is influenced by other factors too though. Clothing can “trap” much of the back spatter depending on the type and layers of clothing and location of the wound. If the wound area is not covered with clothing (like the head) then you can see more back spatter. CSIs commonly see some degree of back spatter on the shooting hand in gunshot suicides with head wounds.
The degree of back spatter on the subject varies wildly though. A number of factors influence the deposition of the blood such as subject and victim body positions, wound position relative to subject, distance between subject and wound, the amount of energy causing the spatter, intervening objects (like shooting through a window), and the presence or absence of blood at the impact site just to name a few! The size of the resulting blood droplets varies too. Gunshots and explosions can produce very tiny droplets (with a diameter of 1mm or less) while other impact events can produce larger droplets from 2mm up to 10mm and even larger. You may find back spatter on hands, faces, ears, hair, clothing, weapons, furniture, or practically anywhere near the impact event. It can even be found on items that have been moved to another room (as in a staging). With gunshots, you may find spatter up to four feet from the impact site. In theory, you could find them even further away if there is sufficient air current such as high wind or even the close proximity of a fan.
So how would you use this in a novel? Back spatter can be washed from hands and clothing or even the victim (think of a dog or cat licking the victim). Tiny spatter is very difficult to see however. You could easily have a detective, spouse, or dry cleaner find these tiny spots on a garment, vehicle seat, or window blinds. If on clothing, consider putting the spatter on something like socks, undershirt, or underwear that would have been covered during the suspect’s version of events (or denial of events). That not only places them at the scene but could also place them in a state of undress at the time of blood loss. You get the picture. Be creative and use your imagination to produce a big plot twist.
Why do criminals choose one house over another?
This is a common question CSIs must address with each crime scene. Why this house? Why this victim? Why me? (just kidding!) We don’t always figure it out but understanding what may have attracted the criminal may provide insight into the type of criminal we’re looking for. Of course, each crime is different. The location may be incidental to the victim but, for the sake of this discussion, let’s just focus on location. To answer this question I generally begin by breaking down my options into two categories; Intelligence and Opportunity.
Intelligence doesn’t relate to IQ. By Intelligence I mean information. This may tie in to what is stolen. I remember a residential burglary once where the owners reportedly had several thousand dollars in cash taken. When I asked where the money had been kept the man took me to the master closet and showed me an older sport jacket (among dozens) that he used to stash the cash in. There were no windows and so it was immediately obvious that whoever had stolen the money knew it was there. Nothing else was disturbed and the odds of a burglar stumbling on the right jacket were astronomical! Turns out his teenager had disclosed (bragged about) the information to some “friends” at school. The point is that they knew what they were looking for and where. The same may be true for drugs, guns, counterfeit money, etc. If your victims are professional criminals (sometimes they do call the cops) they will be less than truthful about what was really stolen. They just want the CSIs to figure out who committed the crime. Criminal locations targeted may include rival drug houses, prostitution rings, money launderers, etc.
Is the home adjacent to a greenbelt or park and lacking blinds or curtains? Can the burglar easily “case” the house at night with the lights on? Does the victim have a predictable routine or habit that is easily observed? Is this the only house on the block without an alarm sign in the front yard? Are they the only ones without a large dog? What makes this house or business more appealing than the one next door? Of course, businesses are somewhat different than homes. They type of business may have everything to do with selection. A gas station or pawn shop is more tempting to a robber than a dental practice. Unless, of course, the dental office is a front!
Opportunity is another factor to consider. Most burglars don’t like to enter occupied structures. So they may be on the lookout for evidence of vacancy. Are there newspapers piled up outside? Solicitor advertisements on the door? Have the trash cans been left on the curb when all the other neighbors have brought them in? These are all passive indicators that no one is home. Sometimes criminals will enter a home. This is more tempting when access is easy such as when the garage door is left open. Some people will leave ground floor windows open as well which are very easy to bypass. Some criminals are even bold enough to ring the doorbell. If no one answers (and they don’t hear a dog) they just go around to a secluded spot and force entry.
So why is any of this important to you as an author? Because readers want to understand the “why” of the scene. Why this house? Why this window? Why this victim? It provides a reasonable explanation to the reader for the actions and motives of the characters. So, knowing how to describe and set up the revelation may bring your reader into a deeper appreciation of the scene. This information can be given in any viewpoint, dialog, or observation of the character. The “how” is not nearly as important as the “why”. So when you’re developing a scene try not to just toss out random elements. Ask yourself why your criminal decided on this particular location and then reveal that in some way to the reader. I guarantee you they are dying to know!
Will Washing Clothes Really Destroy Bloodstains?
Blood evidence is a powerful tool for the crime scene investigator. Whether testing for DNA or examining the bloodstain patterns to reconstruct the events of a crime blood is a powerful witness. This fact is not lost on the criminal. This knowledge is rooted in the old saying “caught red-handed” in which a criminal with blood on his hands was thought to be guilty. So criminals have learned to clean crime scenes and evidence and CSIs have learned ways to recover it. Without getting too deep in the forensic weeds; cleaning efforts usually result in either diluting the blood or masking it. Using a washing machine is an effective way of diluting bloodstained clothing. Criminals also have easy access to washing machines so it’s not too surprising that they may utilize them to wash away evidence.
Some of you may already be asking “why not just throw the clothing away?” It’s a god question but to understand it you have to understand a criminal and what they value. A t-shirt may get thrown away like garbage but if the item is their favorite jacket, sports jersey, athletic shoe, or ball cap then they may just roll the dice. One key thing to remember about all criminals. They will clean a crime scene to a point they do not see the evidence. That doesn’t mean the evidence is gone, it’s just beyond the abilities of the criminal to see it. So…will washing clothes destroy blood evidence? Sort of.
I won’t reveal the current state of DNA detection, suffice it to say that researchers are making breakthrough’s all the time. I’ve written before about the durability of DNA evidence and some of the current case studies and research might blow your mind. On the matter of dilution there are some amazing reagents like Luminol that may detect blood at one part per million. Several years ago I conducted a study to see if we could detect bloodstain patterns on washed clothing. I didn’t have high hopes but I thought it may be possible. The long of the short is that a number of cotton shirts were stained with various bloodstain patterns and then subjected to a series of alternating wash and dry cycles. I used washing detergent with bleach and dried the items in a hot-air clothes dryer. The long of the short is that I was able to detect blood on the clothing after five alternating cycles of washing and drying. At the time I used horse blood and DNA testing wasn’t as inexpensive as it is today so I didn’t address that issue. I just wanted to see if the bloodstain patterns could be detected.
You may want to keep this in mind as you’re developing your story. If your bad guy washes his/her clothing you may want o have your good guy find it. This would also work with victim’s clothing that has been exposed to rain, submersion, etc. If you develop a DNA profile all the better! I certainly won’t criticize you for it.
Bloodstained shirt prior to washing
The same shirt enhanced with Luminol after five wash/dry cycles. Note the shape of the stains have not changed and even the footwear impression is comparable.
Fly Specks and Bloodstain Pattern Analysis
The Flesh-fly
One of the challenges for any bloodstain pattern analyst is determining the origin or source of a bloodstain pattern. Many bloodstain patterns associated with violent acts are the result of a breech to the human circulatory system. This can include gunshots, sharp force injuries, blunt force injuries, expectorate, and others. When examining bloodstains at a crime scene the analyst must take into consideration a number of factors including;
- Pattern area
- Stain size/orientation
- Location of bloodstains
- Evidence on scene capable of producing stains
One type of impact spatter has historically been classified as “high velocity” and described as bloodstains measuring less than one millimeter in diameter. These types of stains are sometimes associated with high energy events such as gunshots and explosions but may also be reproduced by other actions which tend to break up the surface area of the blood droplet. I remember early in my career when an instructor made similar stains simply by “flicking” bloody toothbrush bristles to recreate similar sized stains (albeit in an unusual pattern).
CSIs must also consider other “non-criminal” actions which may create additional bloodstains at a crime scene. One such activity is the creation of “fly specks”. Fly specks can actually be created by two separate and distinct acts. Each act will result in very different looking stains microscopically but can be misinterpreted by the casual observer. One type of “speck” is the transfer of wet bloodstains to a non-bloody surface by various body parts of the fly. Most often this is from the feet but may also include the abdomen. More commonly, fly specks are the result of regurgitation. This regurgitation may look like impact spatter but is commonly associated with a “tail” that does not align with the long axis of the stain and is curved. Though, this may not be easily discerned on clothing. Fly specks are typically not created immediately following death. That is within hours (although a few may be). Generally speaking, the longer the body is associated with insects (days/weeks) the more one may find these types of patterns.
CSIs suspecting insect activity as the blood source usually consider two main factors. The first is location. Flies tend to congregate near light sources. This may be a lamp, window, or even a door crack. Investigators that find numerous small bloodstains in such locations should always consider insects as a possible mechanism. Another related aspect is the absence of any other bloodstain patterns. For example, if one believes that a pattern of small “speck” bloodstains are the result of a gunshot wound then it is very likely that there should also be other bloodstain patterns (pooling, contact transfer, etc.) in the same location. Obviously the victim should have a gunshot injury as well. With regard to lamps and shades; if one finds tiny blood spatter on the bulb or inside surface of the lamp shade, but not on the outside surface, then they might consider flies being the source of the blood pattern. Incidentally, it is common to find dead adult flies in window sills and near light sources in cases of prolonged exposure (weeks/months) in indoor settings where access to the outside is limited (no open doors or windows).
I bring this up because these “non-criminal” mechanisms of bloodstain pattern creation can really throw a curve ball to your characters. Although I chose to focus on flies; other actors include cockroaches, beetles, rodents, and even pets (imagine a dog rolling in a pool of blood, going home and then shaking it off). As an author, consider whether these types of events might create a roadblock or diversion for your characters and plot line. Will these patterns generate a red herring or simply add tension to your character relationships (opposing views)?
