In So What IS Forensics? Part I John Paolucci introduced us to the basics of forensics.
In this post, John will discuss the different types of forensic analyses and comparisons used to help reconstruct events.
By: John Paolucci
DNA is considered the “holy grail” of forensic evidence on TV and a CSI can find DNA on just about anything, upload it into a computer, and POW! Your DMV photo shows up in a hologram suspended above the onlookers’ heads with large windows showing a view of the ocean in the background. Same thing happens with fingerprints. I probably would not have retired if this were the case! It can be said that no two people have the same fingerprints, a claim that does not include DNA because identical twins share the same genetic profile.
Fingerprints are often thought of a secondary to DNA for their capability of making an identification. It is true that the science of latent print examinations and comparisons has often come under fire in the courtroom, but there are many advantages. The fingerprint databases called AFIS (Automated Fingerprint Identification System) are replete with offenders who perpetrated every level of offense. Suspects have always been printed for very minor offenses and their prints stay in the databases with rare exceptions where a suspect is cleared and has his prints expunged from the system.
Also police officers have their prints on file as do private investigators and other licensed professionals. There are very few restrictions as to what can be uploaded into AFIS as opposed to the CODIS (Combined DNA Index System) databases. CODIS requires that the DNA profile to be uploaded is likely that of the perpetrator. In other words, if there’s a shooting at a bar, when crime scene arrives they can’t swab every single used glass and bottle for DNA, the need more specific information as to the general area that the suspect was in where it is more likely that he deposited his DNA on a glass or bottle from that area rather than open season on anything someone took a sip from, at least by New York standards. The bottles can all be processed if that information is unavailable, but Fbio won’t analyze 200 swabs and upload the profiles into CODIS; there are strict regulations about the integrity of data uploaded into CODIS that are monitored by the FBI. DNA cannot be used to identify witnesses, but fingerprints can be collected, examined and uploaded.
So where do we find these hidden treasures? Which of the two biometric identifiers you try to collect will often depend on the substrate that you want to process. Let’s talk about a semi-automatic firearm that has a magazine or a “clip”.
The grips are often a textured surface so that the gun won’t slide out of your hand when it recoils, therefore you would want to process them for DNA by moistening a sterile swab and running it over the grip surface. The trigger and trigger guard are areas that are typically smooth but too small to hold enough detail or “minutiae points” to make an identification from a fingerprint so those areas will be swabbed as well, using a separate swab so as not to create any mixtures of DNA in case the grips were handled by the first responder who may have had to remove the firearm from the suspect or came across the firearm in an unsafe condition, i.e. the hammer is back and could easily cause an accidental discharge, and had to render it safe.
The grooves on top of the firearm or on the “slide” as it’s called are another area that is not conducive to latent print development so again you would want to swab that area for DNA. Now how about that magazine? Nice smooth surface for print development and those “lips” at the top where someone pushes the bullets or “cartridges” into, depositing lots of DNA rich skin cells, and the cartridges themselves! Well yes, but the success rate is remarkably low and fast forward to the courtroom where your only evidence is DNA and/or prints from the magazine.
Can you hear the defense attorney make the claim, “Yes, my client admits that he loaded that firearm, but his DNA and prints were not on the outside of the gun, so obviously it was not him who fired that fatal shot!”? I’m not saying don’t process the magazine, but my job was to defer analysis of the DNA from a magazine because of this loophole and see if other more probative evidence is developed in the case.
Once the DNA has been collected, then the firearm can be treated for the development of latent fingerprints. This is typically done by using cyanoacrylate or “super glue” fuming. The firearm is placed into a chamber or “fuming tent” and the cyanoacrylate is heated until it vaporizes. These vapors adhere to the oils deposited by the human hand and you can see ridge detail from prints develop. Yes, they do this on CSI, but it is MUCH less successful in real life. The chances of getting a latent fingerprint from a firearm are less than 5%! The advantage is that the cyanoacrylate will “affix” the print so it is difficult to wipe away, and if you treat it with powder and have a bad “lift”, you can apply more powder and “relift” the print. The disadvantage is that this process encapsulates the DNA making it difficult, though not impossible, to collect by swabbing. This is why we swab first, then fume.
Substrates such as paper produce very poor if any results for DNA but can be treated with a chemical called Ninhydrin that will turn purple when it bonds to the area that was touched. Currency? As they say in Brooklyn “Fugghedaboudit”! It is just handled way too much to collect anything from a bill of any denomination, but attempts to develop prints will usually be made. Paper is considered a porous substrate, and for paper, the preferred biometric you will attempt to collect or develop is fingerprints. Envelopes have flaps that were more commonly licked, same as stamps and DNA recovery from these areas was very successful prior to the age of “self-adhesive” envelopes and stamps. Flaps and stamps will be tested and there is never a presumption that they were self-adhesive.
Clothing, though also porous, is a whole other category of physical evidence that has the potential to yield positive results for DNA when certain protocols are followed. Let’s use an outer garment like a jacket for an example. Say a perpetrator leaves a jacket behind at a crime scene. Jackets are not usually worn over a bare chest, so the areas to concentrate on would be the cuffs and the collar where there is a constant rubbing against the skin (yes, maybe even a nose wiped on the sleeve, but hopefully it won’t come to that!) Scraping of these areas will readily recover enough genetic material to get a full DNA profile. Now let’s say that the jacket that you receive in the laboratory as evidence was worn by the victim, but touched by the perpetrator. You now have much less DNA to work with from a simple touch than you do trying to get the profile of the wearer, therefore you as the criminalist will need to know as specifically as possible where the jacket was touched. The investigator should be asking those questions and putting the information into the “Request for Laboratory Examination Report” that he or she prepares.
You will need to collect the wearer’s DNA for comparison or “elimination” purposes because the wearer’s DNA will likely overwhelm the suspect’s. We deposit small amounts of DNA all over our clothing by taking it in and out of the closet, folding it, dander and sweat, sneezing etc. In homicide cases obtaining the victim’s DNA is not a problem because the victim’s DNA profile is routinely developed from blood cards collected at autopsy. But if this case is a robbery, you have to get the victim to provide his her DNA in the form of a buccal swab, or a swab of the mouth (think of 7th grade French “le bouche” or mouth) to collect skin cells. The victim’s DNA is NOT uploaded into CODIS, it is kept in the case file at FBio for the purposes of comparisons ONLY. Many people have issues with giving up their DNA because they think that we’ll find out about that illegitimate child they fathered down in Florida during spring break many years ago. Leave that work to Maury Povitch, we are only interested in collecting the victim’s DNA for comparisons – period (not a political period that really means asterisk – period as in end of sentence!) This is called an “Exemplar” or “Reference Sample” and it can only be collected by consent when the victim is alive.
We also need exemplars from suspects, and there are ways to bypass consent. A suspect can “abandon” his DNA by discarding a cigarette butt or drinking container and that is fair game for us to collect. We as investigators must be absolutely certain that the item we collect was in fact the same item we saw the suspect drinking or smoking. If the suspect crushes out a cigarette on a street corner and you go to collect it, but there are 5 other cigarette butts there, that is a do-over. If you collect the wrong item you have given your suspect a get out of jail free card because the DNA will not match your crime scene evidence. There are ways to surreptitiously obtain these suspect exemplars, but if nobody’s buying me drinks, I’m not telling!
I consider myself blessed to have had the opportunity to work in the realm of forensics during my tenure with the NYPD, and I continue to read and attend training to stay current which is no easy task with such a rapidly evolving and complex field. I hope that this paper has been helpful and wish everyone luck with their endeavors. I plan to read everything you all write and look for inaccuracies whenever forensic evidence is mentioned, so keep it real!
He was the first ever to command the OCME Liaison Unit where he vetted and managed all DNA evidence collected in New York City. He developed a strong alliance between the Office of Chief Medical Examiner (OCME) and NYPD and was instrumental in developing new protocols and procedures regarding forensic evidence collection and documentation. He also worked as a Narcotics Undercover and Patrol Officer in the Housing Projects of the South Bronx.
He is currently the president of Forensics 4 Real Inc., and trains students and law enforcement in forensic evidence and crime scene investigations. He also provides consultations with movie and television writers, directors and developers working on real crime shows and dramas. As President of Forensics 4 Real he has provided forensic support to private investigations and traveled to Paraguay where he exhumed a body for the collection of DNA evidence to assist in an insurance fraud case.