Monthly Archives: April 2012
Spotting a stolen vehicle is a handy skill for any detective and as writers we need to know what they would look for. Today I have a post at the Crime Ficiton Collective showing you how detectives and CSIs spot a stolen car. Who knows, maybe you’ll see one sometime and help solve a real crime!
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.
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.
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.
I have written previously on the search for trace evidence from the crime scene and suspect and now it is time to talk about the victim. CSIs search for trace evidence because it serves as a powerful tool to link a suspect, victim, and crime scene together. Many violent confrontations between victim and suspect will result in an exchange of trace evidence. Victims may also retain trace evidence from a crime scene or secondary location. Whether alive or dead there are certain areas that may yield valuable evidence depending on the type of crime and actions of the suspect. trace evidence is generally collected by either swabbing, forceps, or adhesive lifters. Here are a few places CSIs routinely search for trace evidence on the victim.
- Suspect DNA may be found under the victim’s fingernails. Scraping or cutting the nails are the preferred methods for evidence collection.
- Suspect hairs or fibers may also be caught up in jewelry like watches and rings, especially if there was a struggle. Hairs may also be found in the clenched hands of a deceased victim.
- “Touch” DNA may also be found on the victim’s hands, especially if the victim had significant contact with the suspect’s skin during a struggle.
- These locations may also contain soil, fibers, pet hair, or vegetation from one or more crime scenes.
- Victim hair (head and pubic) can easily retain everything from suspect hairs, vegetation, carpet fibers and the like helping to link the suspect, vehicle, or crime scene.
- Victims may sometimes bite the suspect and in the process skin or DNA can be transferred or retained in the teeth or on the lips. In some cases foreign objects like fabric gags, tape residue, even gravel may be found.
Genitalia & Breasts:
- Genitalia may be an excellent reservoir for trace evidence including semen, even after a victim has showered or bathed. Body cavities are generally swabbed to recover DNA but examiners should also consider that foreign objects like knife tips, vegetation, or other items may also be found.
- In some sexual assaults a female breasts may contains suspect DNA which can be swabbed.
- Victim’s clothing can hold trace evidence just like suspect clothing. Shoe tread can retain dirt, vegetation, hairs/fibers, even blood. Velcro straps on shoes (or anywhere else) can also be a great trap for trace evidence.
- Pant cuffs and pockets are also great locations to search.
- Stomach contents. I’ll be writing a specific post soon on stomach contents but suffice it say, sometimes victims ingest things during a struggle which can include suspect body parts or foreign objects.
- Ears and nostrils may sometimes contain hairs, fibers, even soil or vegetation from a crime scene.
- Maggot masses. This is an often overlooked location. When medical examiners or entomologists scoop up large samples (or individuals) of insects they may also inadvertently be collecting hairs or fibers clinging to the insects as they crawl across the body.
Have you ever wondered how evidence is submitted and processed by the Federal Bureau of Investigation. This link will take you to the current (2007) Handbook of Forensic Services. This is the guide published by the FBI for state and local law enforcement agencies. It is a compilation of their policies and guidelines for submitting evidence. It can be pretty dry reading but you may find some of the information useful. If nothing else, it may give you some insight as to the types of evidence handled by the FBI laboratory.
Today I am running a free promotion for my debut suspense/thriller The Scent of Fear for Kindle users at Amazon. If you don’t have a Kindle don’t worry. You can download a reader for your computer here. This has been a labor of love and the initial response has been so great I wanted to give a little back to you, the fans. The Scent of Fear is the story of an inexperienced but tough CSI Sarah Richards who finds herself between the killer she’s pursuing and the one pursuing her. The fast-paced story is inspired by some of the many cases I handled in my years as a criminalist. If you haven’t checked it out you have nothing to lose. If you have, please recommend it to a friend! I am busy writing the second installation and hope to have it out in early 2013. There are a bunch of other authors giving away free books too, I suggest Red Tide by Peg Brantley.
I know all of you have been dying to know the answer to this question right? Well, today you’ll finally get your answer. I’ve got a posting here at the Crime Fiction Collective about this very topic including a cool video. Some of you may be very surprised to see what happens when you fire a gun underwater!
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.
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!
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!
When most authors think about tire evidence at a crime scene they probably think about the actual tire tread pattern. That is obviously a very important (often the most valuable) aspect of the evidence but it is not the only one. It’s one thing to discover that a particular style of tire was found at a scene but tires are mass produced and unless there are individual characteristics present in the impression you may not be able to conclusively link the crime scene impression to the suspect tire. So another type of clue we examine is called the track width. The track width is the distance between the center line of each tire (red). Technically, its the distance between the two axle mounts. In the event one edge of the track is obscured the investigator can measure from the outside of one track to the inside of the other (pink) for the same value.
You see, I could find a number of vehicles with a Uniroyal Laredo P225/75R16 size tire, but vehicles of differnt makes and models may have slightly different track widths. The measurement is not unique to any particular vehicle but it may help eliminate possible vehicles. It’s a very simple measurement to take. Finding track width evidence is more common in rural areas (dirt roads) than urban areas (paved roads) except in Winter where track evidence is much more commonly encountered in both areas. So if a CSI can provide detectives with a track width measurement of say 182cm then the detective can simply measure the distance between the tire centerlines on the suspect vehicle as long as it is in a public place or with a warant. If the suspect track is 175cm then that vehicle was not the one from the crime scene. Like I said, this measurement can’t conclusively link a vehicle but it may eliminate it.