So most of you know that in addition to writing novels I also continue to conduct research in the forensic science. Some of it is probably quite boring but I thought you might find my latest paper interesting. We wanted to see how long after deposition we could detect blood on concrete. Concrete has spread across our world at an exponential rate and to no one’s surprise, CSIs must search it frequently for evidence. Blood is generally considered to be fragile and may “disappear” from sight after a few days. We’d like to get called to a crime scene immediately but that doesn’t always happen. A previous study had found bloodstains outside on a concrete wall about two months after deposition but we thought it may be possible to detect it much later.
We also wanted to test the effects on a completely exposed surface (to the elements) with the possibility of some foot traffic. I suspect that we could detect even older blood in a garage, warehouse, or basement floor. We decided to use the blood reagent Luminol because of its sensitivity to blood (1:1,000,000). Luminol is a chemiluminescent reagent that has a long history of use in forensic investigations. Here is a link to the paper if you want to read it (or need to fall asleep!).
As crime novelists I thought it might give you some ideas for a realistic scene. The technique could be used in any scene where blood may have been deposited. Some examples for your novel could include traffic accidents, drive-by shootings, or any other type of violent crime. DNA analysis would not be possible but your detective or CSI might be able to verify a statement from a witness, co-conspirator, or even a psychic! While our study used an “X” type pattern it is plausible that one may uncover footwear or tire impressions or other bloodstain patterns (like drag marks). It may be a great way to keep your reader engaged in the scene as they “discover” the evidence alongside your characters.
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.
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.
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.
It’s not uncommon to come across some really interesting bloodstain patterns when investigating violent crimes. It’s much less common to come across a single drop that throws you for a loop. This phenomenon was discovered by a friend of mine and has stumped a lot of examiners. Take a look at the picture of the blood stain and see if you can tell how it was formed. This is a single blood drop; the kind you might expect to drip from a bleeding hand. The stain diameter is probably around 12mm-15mm. Can you figure out how this stain was formed? Let the analyses begin…
UPDATE: Okay, looks like a few of you have given it some thought. Some were in the vicinity but, no one quite figured it out. One of the key aspects of any bloodstain analysis is what we refer to as the target surface. That’s the surface the bloodstain is resting on. In this particular case it is a coated mat board that is off-gassing ever so slightly. As the blood dries from the edges in, the gas is trapped and “funneled” into the middle where the blood is forced up. Pretty cool huh? FYI…we’ve never seen this phenomenon at a crime scene; only in experiments.
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)?
At a recent lecture I took a question from the audience regarding casting bloody impressions (footwear and fingerprints) on human skin so I thought this might be an interesting topic to bring to your attention. Bloody prints can be challenging to crime scene investigators, especially on dark colored surfaces. Most CSIs will photograph the prints (maybe IR) or try to enhance them with a blood reagent like Leuco-crystal Violet (LCV) or Luminol. The goal is to lift or transfer the impression onto a lighter material so the unique details can be easily photographed.
I’ve written about casting footwear impressions in previous posts but I don’t think I’ve ever written about casting fingerprint impressions. Regardless, the method is basically the same. I’ve actually done research with bloodstained evidence using various casting materials on surfaces such as concrete, fabric, and human skin. One of the casting materials that reproduced the greatest clarity of detail in the impressions is something you’ve probably had in your mouth; Alginate. Alginate is a common casting material used in dental offices for casting your upper and lower teeth and gums. Dentists put it in trays that you bite down on.
Alginate comes in powder form and is mixed 1:1 with water to make a pancake like batter. The material is then poured/spread over the dried impression and allowed to set for about thirty minutes. Alginate can even be used to lift latent impressions developed with color staining reagents like LCV or LMG. The downside to Alginate is that as it dries it becomes very brittle and shape distorted. That means that your character has to photograph the impression immediately after the cast is lifted from the surface. As you would expect, this material doesn’t work well on hairy areas of skin but areas like ankles, wrists, necks, etc can produce excellent results. You can also use this material to lift fingerprints developed with powders but there are other methods that are better suited for such things. I’ll male a note to do a posting on that at some point in the near future.
So if you have bloody shoe, foot, or finger impressions at your crime scene don’t fret! Your characters do have an option to collect such evidence, especially on dark surfaces like a black leather jacket or multicolored bed sheets. If you have an inexperienced CSI character you could introduce a little tension by letting them forget to photograph the cast and within a few hours they have to work with a warped/distorted and brittle cast.
If you are a regular reader of this blog you know that the examination of bloodstain patterns is a crucial step in reconstructing the events of a crime. A proper examination of bloodstain patterns may reveal such things as the number of bleeding subjects, types or locations of injuries, sequencing of events, movements of bleeding subjects, and minimum number of blows to name a few. One category of bloodstain patterns are what I refer to as contact transfer. Two of these types of stains are called wipes and swipes and they can be very useful in crime scene reconstruction. Here is how the scientific working group on bloodstain pattern analysis (SWGSTAIN) defines them.
A bloodstain pattern resulting from the transfer of blood from a blood-bearing surface onto another surface, with characteristics that indicate relative motion between the two surfaces.
In simple terms this means that a bloodstained item like a hand comes into contact with a non-bloodied (clean) surface and said pattern indicates a direction of travel. Swipes can be used to reconstruct the movement of persons in a scene as well as indicate the location of injuries in some cases. In the picture below you will see a large swipe on a bathroom wall adjacent to the tub. There are also swipe stains on the edge of the tub and the heating vent on the floor. The victim was present on scene so it was pretty easy to correlate the injuries with the swipe stains but had the body been removed (or left on their own power) an analyst could reconstruct the events with some reliability. You’ll notice the area on the wall is quite large and there is an “arch” shape to it. This individual had a large amount of blood on the right shoulder and back as well as both hands. They collapsed against the wall with their right shoulder and slid downward. They also placed a bloody right forearm and hands on the edge of the tub. As a writer you should consider the location of your character’s bleeding injuries. If they have bloody hands and they open a door then they are going to leave stains either on the handle or on the edge of the door (or both). If they are bleeding from a gunshot wound to the leg and drive a car there will be blood on the driver’s seat. If you really want to get serious you can place some ketchup on an area of your body/clothing and then re-enact their actions to see where the staining will occur (note: we would never use ketchup in CSI work but it it easier to clean up then blood).
An altered bloodstain pattern resulting from an object moving through a preexisting wet bloodstain.
A wipe pattern is usually created when an object (bloody or clean) makes contact with a wet bloodstain and alters its appearance in the process. So if you have blood spatter on a wall and then a person’s hand wipes through the pattern it will leave evidence of that contact in the deformation of the original stain. Obviously this is an indicator of sequencing events. The event creating the original stain occurred before the event creating the wipe pattern. Imagine you have blood droplets on a tile floor and sometime after that the victim’s body is dragged across that floor. The original blood droplets may have a skeletonized appearance which may even indicate a minimum elapsed time between the two events. The image below shows an existing mixed passive and impact spatter pattern that has had a clean cloth wiped across the surface from left to right.
As writers you may not want to get into this level of discussion in your storyline but using the proper terminology will go a long way with knowledgeable readers. The important thing to remember is that bleeding subjects are usually going to leave behind bloodstain patterns, especially when they make contact with another surface. Consider how that will look in your crime scene setting and what deductions your characters can draw from it.
As authors, using acronyms gives a little realism to your character dialog and shows that you’ve done some basic research into the forensics profession. So I thought I would define a few of the more common acronyms used by CSIs. Don’t be shy about using these in your novel.
- SLR = Single Lens Reflex. The SLR is a type of camera most CSIs use. These cameras have a detachable lens that can be separated from the body. This is different than the small point and shoot cameras popular with most people.
- ABFO = American Board of Forensic Odontology. A very common photographic scale (ruler) is called an ABFO scale. It is “L” shaped with 6″ arms.
- UV = Ultraviolet. Many body fluids like semen, saliva, and urine will fluoresce under UV light and photographed even if they are invisible to the naked eye.
- IR = Infra-red. Infra-red light is used to detect and photograph various forms of secret writing, different inks used on the same document (like a check where someone adds extra zeros to the cash out amount), and even drugs.
- ALS = Alternate Light Source is a device using both ultra-violet and infrared light to discover evidence.
- UAV = Unmanned Aerial Vehicle. UAVs (also called drones) are becoming more popular with law enforcement agencies as a platform for taking aerial photographs and video. Basically they are sophisticated remote controlled aircraft with camera equipment that can be controlled from a ground based pilot.
- ACE-V = Analysis, Comparison, Evaluation, and Verification. This is the methodology used by fingerprint examiners to compare latent crime scene fingerprints to inked fingerprints on an arrest card.
- AFIS = Automated Fingerprint Identification System. This is a ubiquitous term used to describe a variety of computer databases that store and search fingerprint images. Don’t confuse with AFIX Tracker which is a specific brand of AFIS type computer system.
- I-AFIS = Integrated Automated Fingerprint Identification System. This is the national fingerprint database operated by the Federal Bureau of Investigation that can be accessed by state and local law enforcement agencies.
- CSI = Crime Scene Investigator
- SOCO = Scenes of Crime Officer is the term for a CSI in England
- FMJ = Full metal jacket
- HP = Hollow Point
- DNA = Deoxyribonucleic Acid; our genetic building blocks
- STR = Short Tandem Repeat is a type of modern forensic DNA testing of specific loci on two or more samples.
- RFLP = Restriction Fragment Length Polymorphism refers to differences between homologous DNA sequences and is an older testing procedure.
- CODIS = Combined DNA Index System is a computerized database of DNA profiles used in criminal investigations (similar to AFIS).
- BAC = Blood alcohol content.
- LMG = Leucomalachite green is a blood reagent with a strong odor that turns the latent bloodstain a green color. It is not commonly used today.
- LCV = Lueco-crystal Violet is a blood reagent that turns bloodstains a dark blue/purple color.
- GCMS = Gas Chromatograph Mass Spectrometer is a device used to identify chemical compounds in unknown samples like illicit drugs. It is a great instrument to use with mixed samples or for general screening but it will totally consume the sample.
- LCMS = Liquid Chromatography Mass Spectrometry is another method of drug testing that is useful in complex mixtures of samples.
- FTIR = Fourier Transform Infrared Spectroscopy is a devices used to test a liquid, gas, or solid substance to identify it. It is the preferred method if you want to save the sample or if you need to identify an isomer.
- GHB = Gamma-Hydroxybutyric acid is a common date rape drug that is both colorless and odorless. It is commonly slipped into victim’s drinks.
- SEM = Scanning Electron Microscope is a device using electrons rather than light to visualize very small evidence about 250 times greater than the typical light microscope.
Professional Forensic Organizations:
- IAI = International Association for Identification
- AAFS = American Academy of Forensic Sciences
- ACSR = Association for Crime Scene Reconstruction
- IABPA = International Association of Bloodstain Pattern Analysts
- RMABPA = Rocky Mountain Association of Bloodstain Pattern Analysts
- SWG = Scientific working group (several groups based on field of study like SWGTREAD, SWGSTAIN, SWGGUN, and SWGFAST)
Don’t forget that a lot of agencies have acronyms like the FBI, DEA, BATFE, etc. Also, I have left out a number of acronyms that deal with accreditation and safety as I can’t imagine you wanting to use them in dialog (unless you want your readers to fall asleep in which case let me know!)
Although I am no longer in law enforcement and I don’t work on cases I still conduct research in the forensic sciences. I thought some of you might find this latest article interesting. Criminals may employ a variety of tactics to conceal forensic evidence from CSIs. Some of these efforts can be very effective while others are not. As CSIs we continually push ourselves to discover new techniques to thwart criminal efforts to conceal evidence. As authors, it pays to keep abreast of some of these techniques in your writing. In the article linked above one of the major discoveries was the false-positive reaction with one type of wall paper. This finding supports the idea that wallpapers should be removed to test for neat or latent blood staining underneath. Enjoy.