Category Archives: The Crime Laboratory
Casting Bloody Prints with Alignate
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.
Bloody shoe print from human skin
Cast of LCV Enhanced Print from Denim Jeans
Inkless Footwear Pads
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.
RAM Fingerprint Reagent
Fingerprint developed on pliers
Today I thought I’d cover a interesting fingerprint reagent called R.A.M. RAM is a mixture of three fairly common fingerprint reagents; Rhodamine 6G (R6G), Ardrox, and MBD 7-(P-Methoxybenzlamino-4Notrobenz-2-Oxa-1,3-Diazole). To my knowledge this reagent gained popularity in the early 1990′s and continues to see use today in many crime labs. These reagents are used to enhance fingerprints developed through superglue fuming (cyanoacrylate) followed by inspection under ultra-violet light. All three of the above reagents comprising this mixture are used in fingerprint development so one might wonder; why mix them? Simply put, the mixture can create a broader range and intensity of reactions making photography much easier. Of course, that was more of a concern when lasers and light sources had weaker light output (100w) compared to the units today putting out 500w. Fluorescent dye stains are very practical when processing fingerprints on multicolored non-porous surfaces because the colors of the background surface are muted under ultra-violet light and the fingerprint reagent stands out under fluorescence.
Once the evidence is fumed, the RAM can be sprayed or applied with a squirt bottle. The item can also be dipped in a tray of reagent. There is no need to rinse the item after processing with RAM. The RAM reagent is a yellow color and a little thicker than water in viscosity. Once the item is dried it is examined under ultra-violet light between 415nm and 485nm with the best results usually found at 460nm with an orange colored barrier filter. The shelf life of RAM is approximately thirty days or until certain components like petroleum ether begin to separate and will not reconstitute.
Using a squirt bottle to apply the reagent
Crime Lab Tour: The Forensic Garage
Vehicle examination bays are a relatively new feature of the modern crime lab in the United States. Now there have always been garages that vehicles could be sequestered in but that was not their primary purpose. Large agencies may have used parking structures (for patrol vehicles) or impound lots but they lacked certain amenities for the forensic scientist. When I first got into forensics we used to process vehicles at the tow yard. Some had indoor garages but others did not. In some cases they would back the cars into a kind of shipping container where you couldn’t even open the doors! Another problem is the potential for unauthorized access. Even if you lock the vehicle it’s possible for damage to occur from the normal operations of the tow yard. Workers may brush against the car wiping off fingerprints or they can accidentally hit the vehicle as they move other vehicles around. I’ve even seen cases where the suspect (owner) climbs the fence after hours and literally steals their car back from the tow yard.
A vehicle in a tow yard
A forensic garage offers certain qualities that are hard to find in other facilities such as,
- Security from all persons not affiliated with the investigation (including other officers and detectives)
- Environmental control (weather, lighting, temperature, etc.)
- Access to specialized tools and processing systems.
A vehicle in transit on a flatbed tow truck
Most vehicles can be processed in the field. Fingerprinting a recovered stolen vehicle with no damage may not necessitate it being towed back to the crime lab. If the car was used to kidnap and rape a woman however, it’s going to take time to process. Some vehicles can take hours to properly search and document. It’s nice to have a safe and secure area to work in where you don’t have to worry about approaching snow storms, security, limitations of your equipment, or even the prying eyes of the media. You may have to wait hours for a search warrant to look for various kinds of trace evidence, documenting damage like impacts or bullet holes, or even restoring obliterated VIN numbers so it nice to know the vehicle is protected. A forensic garage allows the investigator to control the environment which is critical for things like an ALS examination (light control) or the application of blood reagents like Luminol.
Looking for a bullet with a fiber optic scope
In addition to the controlled environment the garage can provide very specialized equipment such as chemical fume hoods, vehicle lifts, pneumatic tools, even a winch. Vehicle lifts are handy for getting under a vehicle to recover fired bullets, remove tires or bumpers, or even document things like damage to brake or fuel lines. It’s also nice to get under vehicles to look for blood, tissue, or clothing strips in cases of hit and run or homicide where the victim is intentionally run over. You may even find vegetation from the crime scene wedged in the undercarriage. Most garages are designed to be over sized. Large enough to house a city bus or several vehicles at once. Further, the garages are alarmed, can be easily locked down, and may even have video surveillance. I was recently at a large garage that even had a huge tent structure that allowed the entire vehicle to be fumed with cyanoacrylate! Most forensic garages have room for two to six vehicles although some agencies may have more if they can demonstrate a need (like a regional or state crime lab).
Vehicle on a lift. Notice the chemical fume hood in the corner to the left. These are used for things like fingerprint processing with chemical reagents. The white hose is to evacuate exhaust fumes.
Pink ballistic trajectory rod in a vehicle
Bottom line is that a forensic garage is a unique feature of the modern forensic laboratory. They are nothing like the automotive garages you may be used to. They are over sized to ensure there is enough room for a photographer to be able to get the whole car in a single photograph and some even have cat walks above so elevated pictures can be taken. If you ever get a chance to tour a crime lab call ahead and see if they have a garage you can visit. Some may be off site from the main crime lab so it doesn’t hurt to ask in advance.
A view without a vehicle
Invisible Ink on the Fly
Invisible inks have been around for centuries; used by good and bad guys alike. If you ever thought of using an invisible ink for a scene come join me today at the Crime Fiction Collective to see how invisible inks can be used in a pinch.
What Does A Latent Fingerprint Card Look Like?
Placing lifting tape on card
Have you ever heard a CSI refer to a latent lift card? Chances are you have…but have you ever seen one? When CSIs develop a powdered fingerprint they have to lift it with tape. Then they affix the tape to a card which then allows the examiner to compare it without damaging it (since the powdered impression is protected by the tape). Some people think that the cards just contain fingerprints but that’s not true. Do you know what kind of information is (or should be) contained on it? A proper fingerprint lift card has two sides. Most cards are white colored about 3″ x 5″ card stock type paper. Black colored cards (glossy side) are also available for using light colored powders. Larger cards do exist for full hand or palm impressions as well but these are less commonly used. Generally the fingerprint side has a glossy finish. The other side of the card contains important information for the analyst and the courts. You see, it’s not enough to simply have a suspect fingerprint. You need to have additional value to give it any (legal) weight in court.
One important piece of information contained on the fingerprint side is what we refer to as an orientation arrow. This allows the examiner to orient the print on the object or surface it was lifted from. This helps the examiner determine how the object was touched. Common orientations include “up” (doors/windows), “front” (vehicles), “north” (horizontal plane), or some feature of the object like “towards muzzle” (firearms).
Latent lift card with prints and orientation arrow
The back side of the card contains a lot of important case information like the case report number. This is the unique number that identifies a specific call/location/crime. There are a lot of different formats but most contain a year and sequential number of the call (i.e. 2012-1234 or the 1,234 call to police in the year 2012). The location (address) of the call is also listed. Some crimes involve multiple locations. In a bank robbery you might have evidence recovered from the bank, getaway vehicle, and suspect’s residence for example. These areas may be processed over a couple of days as well so the date and time of collection/development is also important. Was this the print developed on March 20th or April 3rd?. The examiner’s name and badge number are also important for the chain of custody. A CSI may also make a small sketch (say of a car door window) and indicate exactly where the print was lifted. Simply saying it was collected from a window may not give an accurate picture. Was it from the top of the window or bottom? Was it on the inside (private) of the door or outside (public). All of this information is important to better evaluate the probative value of the print. A fingerprint on the outside of a victim’s vehicle may not be as suspicious as one found on the inside.
Back of lift card with case information and sketch. Notice the similar orientation arrow in sketch.
Now sometimes officers get distracted or busy and they forget to mark some or all of this information. This can cause a lot of uncertainty when evaluating the value of the evidence. Here is where it can get interesting for you as a writer. You can use this lack of information to create some uncertainty in your story. Imagine your CSI checks out evidence from a crime and finds a suspect fingerprint. But the card doesn’t say where the card was collected or who even collected it! You can’t even be sure it is associated with the crime in question because there is no case number on it. Isn’t it possible the officer mistakenly mixed it up with the cards from another case at the end of shift when they booked it into evidence? After all, how would they know right? Now this rarely happens and when it does it’s usually on a minor crime. But what if it was a homicide? You know Mr. X’s fingerprint was found, but where? Consider using that seemingly minor mistake to build a lot of tension and uncertainty in your plot.
Touring The Crime Lab: The Fingerprint Section
The fingerprint section is a workhorse of many crime laboratories and much more prevalent than DNA sections. Even small agencies, like university police departments, can have a fingerprint section. Many modern crime laboratories are divided into two broad areas; laboratory and administrative. Administrative areas include the offices or cubicles of the analysts as well as conference rooms, break rooms, etc. while laboratory areas are designed for work with hazardous materials and evidence. Most evidence is examined in the laboratory areas but latent fingerprint cards and fingerprint arrest cards (also known as 10 print cards) might be compared at the analysts desk. As such, I will talk about the fingerprint section in terms of the laboratory area and administrative area.
The Laboratory Area:
This part of the fingerprint section is where all of the physical processing takes place. Fingerprint examiners use a variety of chemical reagents and powders to develop latent fingerprints and need an area to conduct these process safely. Because powders and liquid reagents don’t mix well and the nature of air flow there are generally two types of work stations. The downdraft hood is used for powder processing. This type of hood draws air (hence powder) down and away from the analyst. A filter system traps the powder so it doesn’t get airborne in the general laboratory area. Fingerprint powder isn’t considered really hazardous so using a hood isn’t required. It just makes things less messy.
Down Draft Fingerprint Hood
Chemical fume hood with glass shield
Chemical reagents are used under a fume hood. These hoods have a much greater air flow (at least 100 linear feet per second across the face) drawing the air up and away from the analyst. These fumes are filtered before exiting the building. Many fingerprint sections also contain a photo station with a copy stand and alternate light source so that fingerprints can be professionally photographed as they are developed. Countertops and sinks are generally chemical resistant and dark colored in modern laboratories. Obviously you’ll also find lots of drawers and cabinets containing supplies and chemicals used in this section.
Another common piece of equipment is the superglue fuming chamber. You can see a “bank” of these cabinets behind the man in the video. These fuming chambers expose evidence to cyanoacrylate fumes thereby making the latent fingerprint visible. The fumes are very irritating and these cabinets need to be able to evacuate all of the fumes before the doors are opened.
Superglue fuming chamber
Heat plate and bottle of liquid cyanoacrylate (superglue)
The Administrative Area:
One would think that most of the work in a fingerprint section is done in the processing lab. However, examiners spend most of their time doing comparisons and computer searches through AFIS like systems. These areas may also contain printed arrest cards from suspects arrested by that agency (as well as employee fingerprint records). This work might be done at the examiner’s desk or a shared workspace. Either way it is a typical office setting. AFIS terminals are best housed in a room separated from other sections so that the lights can be turned off. This allows the examiner to see the screen images with better clarity.
Examiner using an A.F.I.S. computer
Sorry Guys…Size Does Matter
Sorry….I couldn’t help myself. In the world of forensics this is an important realization though. CSIs have to measure a lot of stuff. This is especially true for forensic scientists who deal with comparative analysis. This is the comparison of individual and class characteristics between known and crime scene (unknown) evidence or sources. This includes comparisons of footwear and tire impressions, tool marks, even comparisons of things like nails or ball bearings used in a bomb. Other fields like photogrammetry also are highly dependent on the use of scale. The reasons go beyond accuracy and serve as a way to ensure that we’re comparing apples to apples as it were.
In order to demonstrate scale CSIs typically use a particular type ruler designed for forensics. They come in 6″ or 12″ lengths and some even have 90 degree arms on them so the printer can account for adjustments in all three dimensions. You see, if we don’t use an appropriate scale or worse, no scale at all, we may not be able to compare one item to another. Think about it. If I take a photograph of a shoe impression in the mud how can I demonstrate it has the same dimensions of a suspect shoe without a scale (or a cast in that case). Some laboratories actually have to have their scales (rulers) certified by the state weights & measures bureau or similar agency annually. Some of this is too technical to really add to your storyline but there are some aspects that you can use in scene development.
Proper forensic scales
Obviously, CSIs don’t respond to every crime scene. That being the case, officers are equipped with point and shoot cameras to document minor crime scenes. They are taught to use a scale but sometimes that just doesn’t happen. Officers have lots of excuses like they couldn’t find the scale in their kit, they lent it to another officer, or at times they just forget with all the other crap they have to deal with. When that happens the officers sometimes get a little creative. I’ve seen them use everything from car keys to sharpened pencils or coins. Now you might think that a coin might be a fine scale but the problem is that while you can calculate the size of the coin you can’t tell if the camera is at 90 degrees and when you scale a photograph you run the risk of introducing a lot of error over larger distances. It might work alright for a bullet but much less so for a tire impression. More to the point it just doesn’t look professional. Sometimes even the “professional” criminalists do goofy things. I remember seeing a case presentation from an investigator from a very poor jurisdiction actually use beer cans from the murder victim’s refrigerator as a scale for the suspect’s bloody shoe prints. I remember sitting through the presentation thinking it was satire (as did others) only to discover he was serious!
Improper forensic scales
So how can you use this in your story? Well, I’ve already touched on it. If the field investigator doesn’t use a scale on a shoe impression (and doesn’t cast it) it can be the best photograph in the world and it would be basically worthless in associating a suspect to the scene. This can create a lot of tension between your characters and force them to look for other evidence if they want to catch the bad guy. So as a tool to create a great obstacle think about having a character make such a mistake. Remember…size does matter!
Soil impression with scale
The Amido Black Blood Reagent
There are a number of other blood reagents like Luminol, Fluorescein, and Leucocrystal Violet that seem to be much more commonly referred to in literature and on television but Amido Black is another one you might consider using in your story. Amido Black is a presumptive blood reagent (can’t discriminate between human and non-human blood) that is very useful in developing diluted or latent blood impressions like shoe prints. This makes it an effective tool in the bloodstain pattern analysts arsenal. Amido Black is a water or methanol based dye stain that reacts with the proteins in blood turning them a dark blue-black color). The process begins by “fixing” the possible blood impressions with a methanol wash prior to the application of the reagent. Sometimes this methanol is mixed directly with the reagent at the time of application. The solution can then be sprayed or poured over the testing area. Some smaller items of evidence can be “dipped” in trays of the reagent as well. The reaction may not be as “flashy” as one of the luminescent reagents but it can be just as effective.
The sensitivity of the reagent is thought to be about 1:10,000 (parts per blood dilution) and has no detrimental effects on subsequent DNA testing although if too much reagent is “washed” over the evidence the sample could become too diluted for DNA testing. It can be used to detect any latent mark (such as tire print, shoe print, fingerprint, or tool mark) in blood at the crime scene. Once the reagent is applied and the blood impression is developed then the visible impression needs to be “fixed” with a 5% sulfosalicylic acid. The print can then be photographed.
I have successfully used this reagent many times at crime scenes and in the laboratory. It provides exceptional detail provided there is contrast with the background. That is the one potential problem with this reagent. Because it turns the blood a dark blue-black color, you can’t use it effectively on dark colored surfaces. That is something you’ll want to keep in mind if using this reagetn in your novel. The video below presents a homicide case in which Amido Black was successfully used to develop bloody shoe impressions from the suspect at the crime scene.
Touring The Crime Lab: The Photography Lab
Photographic labs have undergone tremendous changes since the adoption of digital technology. For the edification of our historical writers I’ll try to paint a brief picture of the largely extinct film based labs. When I first began my career photography labs dealt with film. We used primarily 35mm color but occasionally dealt with Polaroid and Medium format cameras as well as specialty films like infra-red. Photographic film is, of course, sensitive to light. Controlled exposure to light (by proper apearature and shutter speed settings) is how a picture is imparted onto the film. That being the case, photographic laboratories contained a darkroom. A darkroom could range in size from a small closet to a 500 sq. ft. area but they all had one thing in common and that was the ability to be “light tight”. That means no windows and seals around doors to prevent “light leakage”. Some rooms even had neat revolving doors which were round spaces about 4 feet in diameter with a 2/3 sized opening which kept light from entering the darkroom as the technician entered the darkroom.
Revolving Darkroom Door
Developing film requires one to process the film through various chemical developers and washes (developer, bleach, fixative, wash). Prior to the 1960′s this was largely done with trays of chemical solutions. The photographer would take the film and dip it in each tray for a predetermined period of time until the image was developed and then hung to air dry. As police began taking more photographs it became necessary to automate this process. These machines contained tanks of the necessary chemicals and a conveyor belt like system to drag the filmstrip through the chemical at a predetermined speed (exposure). The rollers on these machines had to be cleaned everyday to keep the accumulated chemistry from building up and possibly scratching the negative. It was messy and smelly. One colleague actually worked in the FBI photo lab back in the Hoover days and was required to wear a 3-piece suit while working with these chemicals!
Wing Lynch Film Processor from the 1980's
Working in a darkroom takes skill. You would have to be able to break open the film container, attach the film to leader cards, and feed the cards in complete darkness. Some labs used red lights that in theory didn’t harm the film but most did not. Needless to say we used small tabs of glow in the dark tape to highlight tools and latches we had to find in the dark. I stubbed a lot of toes and banged a lot of knees. There would be one piece of equipment for processing film and another similar machine for printing the image onto paper. Each of these could be 4′ high x 2′ wide x 6′-8′ long. Later versions (C-41) could be used under normal lighted conditions with the invention of certain loading devices that could extract the film from the canister without exposing it to light. But starting in the mid to late 1990′s the digital wave took the industry by storm making these darkrooms largely unnecessary (although some labs still use a large printer for printing large numbers of digital images onto paper).
The modern police photo lab is pretty simple by comparison and doesn’t require nearly the same amount of real estate. Images are processed and stored on a computer instead of the old large processors. Again, in the old days you had to have huge file drawers or cabinets to store all those film negative strips. One piece of equipment that has survived the transition is the copy stand. The copy stand is a mounting system that allows the CSI to mount the camera on a perpendicular plane to the evidence being photographed. Most have adjustable arms with lights for oblique lighting as well.It’s very handy when doing close-up photography where you need a steady platform. It also frees up your hands to operate other equipment like an ALS.
A copy stand with "evidence" perpendicular to the camera image plane
Modern C-41 Film Processor
Another area that is commonly used is the “privacy room”. CSIs sometimes have to take pictures of sensitive areas (genitalia) from living victims. You can’t just ask them to drop their trousers in the main lobby right? You need a place that respects their privacy. That means no windows. Good photographers also like to use an industry standard 18% Grey colored background. This is the grey color you see in a lot of modern mugshots. The specific color allows photographers to calibrate the accuracy of the colors when printing. You can have the paint mixed to that color at any hardware store and simply paint the walls. It’s inexpensive and very effective. Some labs also use colored “curtains” or backdrops similar to what you might find in a commercial studio for the same effect.
Like any other room in the lab we still need plenty of drawers and cabinets to store the various lenses, filters, camera bodies, scales (rulers) and other nifty tools we use while photographing evidence and people. More sophisticated labs even have posable mannequins for use in displaying items of clothing or reconstructing body positions in reconstruction for court exhibits but that is a topic for another posting!
