Ask a forensic scientist anything jobstr

Okay, #1 biggest: We do not really have a BatComputer! Do you remember the episode where they poured in alphabet soup and it spelled out a message? Real scientific instrumentation does not work that way. We don’t have a machine that can accept any type of animal, vegetable, or mineral and tell you exactly what you want to know about it. Instruments might analyze organic material or inorganic material or, like my infrared spectrometer, inorganics but only within certain parameters. For example my atomic absorption spectrophotometer was set up to detect barium, antimony and lead on shooter’s hand swabs. The hand could be covered in arsenic and I wouldn’t have any way to tell. Materials can be run against a database of similar materials, yes, but databases exist because some lab tech went around rounding up samples of nail polish and created their own.


There is no national database of perfume or wall paint or cat food–and even if there was, those items change formula every couple of months. So even if I can easily determine that this fiber is, say, nylon 6,6, there is no database that’s going to tell me that it comes from a Halston sweater sold only by Macy’s and this is how many they sold in this area and this is who they sold them to and, oh, here’s a driver’s license photo. Companies do not publish their formulas and stores do not hand out their sales figures (and we certainly cannot ‘hack in’ and get them). That would most likely be violating SEC and civil liberty laws. Okay, enough of that rant.

#2: Someone like me in Smalltown, Anystate, cannot scan in a latent fingerprint (from a crime scene) and search everyone who has ever been fingerprinted in the entire United States including job applicants and military. Most databases are local, maybe statewide depending on where you are and your software. I can search people arrested in my town, and have been receiving those from the county for a number of years. I do not have access to job applicants, not even our own, and certainly not military. That said, I estimate that in five to ten years I will be able to electronically submit a limited number of latent prints to the FBI’s national database, but certainly not yet and certainly not for the past 50 years, as TV shows would have you believe.

Those are the two biggest. Oh, and we very rarely package evidence in plastic, we don’t wear skin-tight, designer clothes and high heels to crime scenes (when you work around blood, bleach, dirt and decomp fluid you never wear anything that you’d be upset about if it got ruined), we don’t interview suspects or tell the cops who to arrest, and we’re not all young, single, sexy and angst-ridden. We’re really very ordinary. Though I understand that doesn’t make for the most captivating TV character.

This is certainly possible, but would be a very iffy way to frame someone. First you have to talk this other person into cooperating while you make a mold of their finger. THen you can use some epoxy based putty to cast the finger. Provided this goes well the pattern should be an exact duplicate, so that’s good. Now you have to coat that with something to form a fingerprint. Don’t use your own sweat and oils in case we do touch DNA on the print. On CSI they used cooking oil spray, which might work but depending on how long or short it is until the print is processed, it might be too soft and just smear when the tech powders it. Then you have to put this cast finger to a piece or pieces of evidence that you are SURE the crime scene tech will print. This is where it gets tricky. Say you stage a break-in and you put it on the window frame or broken glass. Maybe the frame is too rough to hold a decent print, maybe the tech fingerprints 15 pieces of broken glass and then gives up. Maybe you take great pains to put it on the murder weapon and then a traumatized witness or a clumsy tech smudges the print when they pick it up. Maybe you leave it on a note in the victim’s pocket (paper is also very iffy!) and then EMS cuts the shirt off and leaves it in the driveway or throws it out in the ER or it gets soaked in blood. THEN when the tech lifts the print, it needs to look consistent with the ‘background’ from the item and the manner in which it was gripped. Of course if the rubber flakes off into the print that might get more attention than you want. THEN if we decide to do DNA analysis on the print (which is possible even after it’s been processed with powder or superglue) the DNA results might be utterly negative or show animal strains (?) or whatever. Again, that might raise a red flag with an analyst, or they might simply figure that there wasn’t enough sample to get a profile. So you MIGHT get away with it. Or you might not.