Category Archives: The Crime Scene
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!
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.
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.
There is an age old tradition in some cultures to fire celebratory shots into the air on certain anniversaries, events (weddings), or accidents. In the United States this activity seems more concentrated around our Independence day and New Year’s Eve (although pretty rare overall). For the purposes of this posting we’ll just consider bullets fired from small arms as opposed to artillery shells. Bullets falling from the sky are no laughing matter. They can cause serious injury including death. But, there are some misconceptions surrounding the lethality and velocity of bullets returning to Earth.
One of the most common misconceptions is that small arms bullets will return to the ground at the same, or greater, velocity than when emerging from the muzzle of the weapon. Now bullets come in a variety of sizes (caliber) and shapes. Basically they are conical in shape but the nose can be flattened or rounded as can the base (to a lesser degree). Believe it or not a number of studies have been conducted on this issue since at least the early twentieth century. It was found that some common rifle calibers such as the .30-06 attained a muzzle velocity of 2700 feet per second and gained an elevation of 9,000 feet. When a bullet is fired straight up into the air it will continue on it’s flight path until it is overtaken by gravity and begins to free-fall back to Earth.
During this fall the bullet will be affected by air resistance. Now it is theoretically possible the bullet can return one of three ways; nose first, base first, or tumbling. Of the three, a nose first return from a near-vertical trajectory is the least likely. It is much more likely that the bullet will tumble or fall back in generally the same orientation (so base first) especially if it retains any of the gyroscopic spin imparted from the barrel (rifling). Tumbling creates the greatest amount of air resistance so the bullet’s terminal velocity will be lowest in this condition. Regardless, most lead core bullets will return to the Earth in about 45-55 seconds. The falling velocity will be determined by a number of factors including the air resistance and bullet weight. Generally speaking, a smaller bullet like a .22 short will have a lower free falling velocity than a larger one like a .30-06.
While the muzzle velocity for most small arms can average around 1,000 feet per second that same bullet may only reach a free-falling velocity of 150-250 feet per second. If you consider that a bullet needs to reach a velocity of approximately 200-330 feet per second to perforate human skin in a nose first orientation you can see how these falling bullets may not cause a fatal wound. The key words being “may not”. There are plenty of case studies of people being killed by downward arching bullets (though some are not at near vertical falling angles. They can still be very dangerous and cause serious injury. They will typically cause less trauma than one fired at close range however.
Reconstructing the original trajectory is nearly impossible because of all the conditions (wind, air resistance, tumbling, original load conditions, etc.) during flight that can alter the bullet path. So if you are thinking about using a falling bullet in your novel you might want to keep some of this in mind. A falling bullet might only pierce the skin or in some cases just create a bruise. In other cases it may actually cause death. The important thing to remember is that they are not traveling at the manufacturer’s listed muzzle velocity. It should go without saying that you should never attempt to conduct this type of research or experiment. All of the published studies I am aware of were conducted by the military on large scale controlled firing ranges. Do not try.
Forensic audio analysis has been around long before the Watergate tapes and continues to make advances. But a monumental leap forward occurred about a decade ago right here in Colorado. You see, one of the foundational elements of any analysis is that of authentication. Edited and doctored recordings should always be considered when reviewing audio evidence. It’s more than just verifying the identity of the source. The source being a person or activity like a gunshot, car horn, or mechanical device. It’s also about verifying the date and time of the recording. Was it made just before the commission of the crime or a year earlier? Sometimes the words said are not as important as when they were uttered. It is the when that helps detectives put things in context. It turns out that within virtually every audio recording there is a silent witness.
There is something called the mains frequency. Inaudible to our ears it is a persistent hum generated by our electrical grid. Amplify the sound and you’ll hear a metallic buzz. Researcher Dr. Catalan Rigoras discovered that this hum fluctuates as the load on the power grid goes up and down. Think of it as a melody of notes arranged in an ever changing symphony. Since the load on the electrical grid is constantly changing, so too is the frequency of the hum. So forensic audio specialists and other researchers have embarked on am ambitious project to record this hum every second of every day and cataloging the signatures in a searchable database. It’s called Electric Network Frequency (ENF) analysis and they’ve been doing it for years. So if an audio recording is made anywhere near an electrical source it will record the hum as well. It can be an electrical outlet, a lamp, computer, anything. The distinctive hum signature acts like a time stamp or watermark. It is unique to that moment in time. The longer the recording the more easily it can be authenticated.
The hum is unique to the power grid so it can get a little more tricky in countries with multiple grids in service. But if a single grid is in use the value of the analysis increases dramatically. Say for instance that someone cuts and splices pieces of audio together…the hum signature won’t match. There will be gaps in the hum when compared to the source hum in the database. What happens when two different audio tracks are combined to make a fake original? There will be two hum frequencies in the background. So unless your recording is made in the desert or the middle of the forest the recording will likely contain the distinctive hum in the background. You might want to consider using this technology in your novel. Whether your character is talking on a cell phone or being recorded on a surveillance system the hum will be there. The key is to use some kind of doctored recording. Your protagonist can then do the ENF analysis to show that the recording has been tampered with (or is original). Either way its a really cool technology.
How many times have you watched a police television drama unfold with the detective asking whether there were any signs of forced entry? It’s one of the most common initial questions in burglaries, home invasions, rape, and murder. If there was no evidence of forced entry then the speculations abound as to whether the suspect was let in, had a key, or made entry by deception. While there are ways to enter a dwelling without force (which I’ll cover later), today I’ll touch on some of the more direct methods and what evidence is left behind. There are only so many ways to enter a dwelling and most suspects use the obvious routes; doors and windows.
The most common method of defeating a door is the frontal kick. Many times this involves the suspect kicking the door near the knob or handle in an effort to defeat the bolt. It’s not as easy as it looks on television and many crooks will have to kick the door repeatedly to force it open. Another similar technique is called the “mule kick”. The suspect faces away from the door and kicks straight back near the bottom of the door to achieve the same result. They are trying to dislodge the molding around the door frame and forcing free the bolt. In either case you will find shattered pieces of the molding on the floor inside the door and the deadbolt (if engaged) will still be thrown open. With either technique you will obviously be looking for shoe impressions on the door (either midway or low) which may require the use of side lighting.
Another common method is to “shoulder” the door. As it sounds, the suspect rams the door with his/her shoulder in an effort to force the bolt through the frame. If the door or clothing is dirty or wet you may find fabric impressions. In all of these cases (kicking or shouldering) it is common for the suspect to ring the doorbell first. They want to know if anyone is home or if there are any large dogs they might encounter. So swabbing the doorbell might yield a suspect DNA profile. If the surface area of the doorbell is large enough you my even get a partial fingerprint impression.
Doors can also be pried open with the use of a tool like a pry bar. These tools may leave impressions in the door frame which can be compared to the class and individual characteristics of a tool should one be recovered from a suspect. These pry marks may also indicate the type of tool used (screwdriver, knife, pry bar, etc.) and link that crime scene to others where similar tools were used to gain entry.
Less common is the use of a ram. A ram can be anything from a sledge hammer to a vehicle. Vehicles are more commonly used in retail business theft. You have probably noticed stores with large cement pillars outside their front doors. This is to prevent someone from literally driving through the front door. This technique is most commonly seen in thefts from gun stores and jewelry stores. The suspects want to get in and out very quickly after the alarm is sounded and a vehicle (usually stolen) is ideal for smashing through heavy doors and iron bars. The stolen goods are then thrown into the car for a quick getaway before the police arrive (they hope). Of course using a vehicle in such a violent manner is akin to a traffic accident and the suspects may leave behind paint transfers, tire impressions (on the broken glass) and even broken pieces of the vehicle that can be later matched.
We often take windows for granted but unless they are bullet resistant, they don’t offer much protection from bad guys. Assuming they’re locked, a window can be defeated with a simple rock. Usually a landscaping rock from the victim’s own yard! You may be able to get a DNA profile from the rock and on a few occasions I’ve even gotten fingerprints. Suspects entering through a broken window can cut themselves (leaving blood) or catch skin or clothing on the broken edges of the glass leaving behind trace evidence.
Walls and Roofs:
Less common points of forced entry are walls and roofs. These avenues generally require more time and effort but sometimes the bad guy figures its his best way in. A wall can be breached with a ram (as mentioned above) or by cutting with power tools. Roof access is usually through dislodging a vent or small HVAC unit. Sometimes they will smash through a chimney to gain access to an attic or mechanical space. The it is just a matter of smashing through the ceiling. Of course, some suspects forget the ceiling is high above the floor and may suffer serious injuries in a fall. Like the guy in this video they may find themselves locked inside the building with no easy way out. This guy actually had to wait for the cops to arrive!
From time to time I get questions about what happens to cartridges when they are exposed to fire. Some people mistakenly believe that cartridges exposed to fire will explode and project the bullet as if it were in a firearm. This is not the case (unless the cooked off cartridge is actually chambered in the firearm at the time of the fire. Even in such events the firearm will not cycle another round (in semi-auto weapons) because there isn’t anything bracing the firearm during blow back. Hollywood has taken quite a bit of license when depicting these events so I thought you might enjoy this (rather long) video showing what actually happens when cartridges are exposed to a number of fire events. Fire fighters have to deal with all kinds of hazards when fighting fires but retail ammunition is not nearly as dangerous as other hazards even though it does sound terrifying when it goes off. After watching the video I was wondering about the first experiment with the custom mount for the cartridges. I wonder if “anchoring” one end of the cartridge actually intensified the reaction because it restricts movement of the cartridge.
It’s Winter in Colorado which means that criminals will be leaving plenty of boot impressions in the snow. CSIs face certain challenges when dealing with snow impressions. Snow is not a forgiving medium. It is difficult to photograph due to its reflective qualities and it is even more difficult to cast in. Snow comes in as many varieties as criminals I suspect. Some methods, like sulfur casting, may work well with certain snow packs while others do not. Sulfur casting presents it’s own challenges and many agencies seek a simpler solution to snow casting. One such method is casting with an aerosol wax commonly referred to as snow print wax. This wax is designed to be used with dental stone. Dental stone is an excellent casting material but it can not be poured directly into the snow. It is much too heavy and as dental stone sets it generates heat. This heat will melt the snow impression detail before the dental stone has a chance to set.
In order to use dental stone in snow you have to build a protective base layer. This base layer will capture the detail of the impression and serve to protect it during the curing process of the dental stone. Snow print wax creates such a barrier. The wax comes in a can and is propelled by an aerosol in the same way spray paint works. Once the snow impression is photographed the reddish wax is sprayed above the impression in short sweeping motions so that the wax drifts down onto the impression. Spraying the wax directly into the impression can damage the fragile features from the force of the propellent.
Snow print wax is not perfect though…far from it. The wax can not be allowed to freeze which means you can’t leave it in your crime scene vehicle for weeks on end. Most CSIs will keep it in the lab and even lay it on the dash over the heating vents on the way to the crime scene to ensure it works properly. Even in the best of circumstances the wax may clump together and sputter larger elements onto the impression instead of a finer mist. When that happens you run the risk of damaging or obscuring details in the crime scene impression. One might wonder then, why use it at all? The simple answer is ease of use. Add to that the fact that many CSIs are not accustomed to casting in snow and it’s easy to understand why they may choose snow print wax. It’s as easy to use as spray paint.
The wax is applied to the impression one shallow layer at a time until all of the impression is covered to a depth of about an eighth of an inch. You have to spray from multiple angles to ensure that all of the snow is coated (vertical and horizontal planes). The wax is allowed to dry about five minutes between coatings and I find that four or five coatings is enough in most cases. After the final coat is allowed to dry the dental stone can be mixed (with very cold water) and gently poured into the impression. In freezing temperatures it may take an hour or two for the dental stone to fully set. Once it has, the cast can be lifted from the snow pack and booked into evidence.
Footwear impressions can provide valuable information to the crime scene reconstructionist. Examiners look for class and individual characteristics in crime scene shoe impressions that may link that impression to a particular suspect shoe. In order tom compare a crime scene shoe print to a shoe though, it’s best to make an impression from the suspect shoe. There are a number of ways to take footwear impressions. One can use black ink or fingerprint powder but, a novel method is the use of an inkless pad. The process involves a pad coated with a special “ink” and chemically treated sheets of paper large enough to hold a boot impression. They work great for footprints as well (no one has yet developed one for taking tire impressions). The ink pad is generally yellow in color, odorless, and can be used for several hundred impressions before it needs replacement. You have to use the chemically treated paper however. The process will not work with standard bond paper because of the chemical treatment. The paper isn’t cheap either. A pack of one hundred sheets costs about forty dollars (US). Initially, the inked impression may appear green in color but will dry black. This provides the highest contrast with the white paper.
This process is well suited for taking elimination impressions. Elimination prints are those from people who may have been in the crime scene but are not suspects. This includes victims, family, customers, employees, etc. The inkless method means you don’t make a mess of everyone’s shoes or run the risk of them tracking traditional ink or fingerprint powder all over the crime scene. It also means you can take very good impressions without having to collect the shoes. Now occasionally, a victim will be wearing shoes very similar to the suspect. In such cases the CSI will have to collect the shoes and book them in as evidence unless they are easily distinguished in size. For everyone else though, this inkless method works very well. All of this is in addition to photography of course. You might be asking yourself…why take impressions if you’re taking photographs? The simple reason is that an impression is a full scale representation of the outsole. Photographs may be slightly out of focus or at an odd angle so that when you enlarge them to life size they do not align correctly. The link below is to a short video demonstrating this process. The only thing I would add is that it is better to wear the shoe and step onto the pad. The weight of the body imparts a better impression in my opinion.