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Some Commonly Overlooked Evidence for Fingerprints

Burglary bag

CSIs love finding fingerprints. A fingerprint is conclusive proof that a particular person touched a particular thing. One may still argue just what inferences, if any, you can draw from that contact but the contact is a fundamental building block of those discussions. Investigations are built upon linking suspects, victims, and crime scenes through the analysis of physical evidence. So it stands to reason that CSIs will make reasonable efforts to process items that may yield a suspect or victim’s fingerprints.

But since we’re authors and we want to add a little intrigue and suspense to our story I thought it might be interesting to talk about some items that may yield fingerprints but sometimes get overlooked. This way, your hero or heroine can swoop in and pull a Colombo to save the case! At this point you might be asking “how does evidence get overlooked?”. Evidence isn’t supposed to be overlooked right? But understanding how and why some evidence is missed may help you with setting up the scene.  In most cases people miss evidence because of a lack of experience. Think of the rookie officer who has only been on the job for a few months. How they approach and view evidence will be drastically different from the fingerprint examiner with 20 years on the job. To a much lesser extent the examiner may be limited by a judicial order as to what they can seize and examine but if the analyst sees something they feel is important at the crime scene they can apply to amend the warrant or get a new one, so that is typically just a temporary roadblock.

Keep in mind that you don’t have to always find the suspect’s fingerprints. Finding the victim’s fingerprints on something in the possession of the suspect can be just as telling.  most of the items that I have noticed get missed are what I’ll call “items within items”. Here are a few examples.

  • Batteries inside a flashlight or other electronic device.
  • Components of a gun (like the barrel, inside of the frame, recoil spring rod, magazine, or other items handled while cleaning). Some may argue that the presence of gun oil and the manner of cleaning makes finding fingerprints unlikely but I have seen prints in these locations. Remember a criminals usually just wipe off the outside of the gun, not the components within.
  • The metal tape inside a standard rolling tape measure. Burglars use burglary tools and often steal those tools and bags from their victims to add or replace tools in their collection. I once had a case where we arrested a burglar and I had to process his tools to see if we could link them to any previously reported theft. Most people don’t engrave their tools so I relied on fingerprints. one of the items in the bag was a 25′ metal tape measure. I doubt the burglar used it for crime, it probably just came with the bag he stole. Well I rolled out the tape to its fullest extent and way back at the 23′ something point I found a victim fingerprint from a major home burglary several months earlier that we now had a suspect for.

Another similar type of location is what I’ll call “out of sight, out of mind”. These are locations that have more to do with suspect behavior and activity than they do with the actual item. Crime is not a static event. Crime is composed of a series of events dictated by various conditions and behavior of the actors involved. Sometimes criminals have a lot of interaction with the evidence or crime scene environment. An example would be a pair of teenagers who break into a house whose owners are at work or on vacation. They might actually make themselves at home for a short while and consume food, beverages (liquor) or see what’s on television. Even in violent crimes like a rape the suspect may pause during or after the crime and help themselves to a beer from the fridge. Like most people, when they are done they throw it in the trash. So here are a few examples.

  • Trash can be easily overlooked as it is easy for officers to become fixated on things like the point of entry, the dead body, blood on the floor, etc. Victim’s may sometime (on instinct) do a little cleanup before police arrive and unintentionally pick up important evidence and toss it before they even realize they’ve been victimized. The of course, in the heat of the discovery, forget to tell officers they found something in the driveway and tossed it in the can.
  • Vanity mirror on the passenger side of a stolen vehicle. I can’t tell you how many times I’ve gotten prints from the suspect’s girlfriend from this location.
  • Porn. Let’s face it, suspects may search a residence in a similar manner to the way police do. In doing so they may discover the owner’s stash of magazines or videos. There is something about the allure of a pornographic DVD case or magazine that draws criminals like a magnet.  Even if the content is something they find gross or offensive they just can’t help but take a peek.

The best way to decide how to use evidence like this in your story is through the use of role-playing. Take some time and imagine what your bad guy has to do to accomplish the crime and what actions they take while there. Also, remember that all items have a history. Undisturbed fingerprints can persist for years and serve as a valuable tool to link a previous victim, friend, or family member of the suspect.

Recovering Erased Marks from White Boards

Erased Dry Board

If you work in an office or school you probably use a white “dry-erase” board. These are commonly found in a variety of settings for presenting information to a group and keeping it posted temporarily. These modern chalkboards offer the advantage of multiple bright colored inks that can be easily erased with a common chalkboard eraser pad. In fact, police agencies frequently use these boards in a “war room” to keep track of changing information during the initial hours of a major investigation. When the case is over the board is erased. To the naked eye it would appear that the information is permanently lost but to the trained CSI it is merely “hidden”. CSI’s love hidden evidence because it represents a challenge; kind of a dare on behalf of the criminal.

You see, some criminal organizations use dry-erase boards too. It might be a chop shop dealing in stolen vehicles, an illegal drug operation or prostitution ring keeping track of customers, financial, or operational (names of prostitutes and locations) information.  Sometimes the information may be patently criminal, other times it is merely another lead to be followed up on. But when the police pound on the door rest assured a criminal will be erasing the board and the information on it.  In that moment they believe they have destroyed the incriminating information.

A well trained CSI however, knows that the information is just waiting to be uncovered. You see, as the marker ink sits on the board it forms a “film”. The longer the ink stays on the board the more hardened the film becomes. When the suspect passes the eraser pad over the writing they are merely wiping off the “color” or pigment. The simplest method to develop the latent film is by the application of standard fingerprint powder with a brush, just like you would process an item for fingerprints. The best part is that the dark fingerprint powder contrasts very well with the white board making photography much easier.

Developed Writing with Black Fingerprint Powder

This processing can be done many months later as long as the board is not wiped with a liquid cleaner. This gives your detectives time to possibly chase other leads or have your protagonist come in later and save the day by discovering the evidence right in front of them. You may even use something like this as an explosive scene in a courtroom drama by exposing the new evidence mid-trial! Play around with some options and have fun with it.


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