The analysis of DNA evidence has come a long way in just the last decade. I always teach that science does not solve crimes, only investigators can solve crimes. Say your DNA evidence gets uploaded into the CODIS databases and it comes back to a convicted offender named John Paolucci. You have a DNA hit, the holy grail of forensic evidence, but your job is far from over. Who is John Paolucci and why was his DNA in your crime scene?
It could turn out that John Paolucci is a relative or close friend of the family who served his time and is out now, regularly stopping by the victim’s residence to drink their beer and tell stories about prison. It could also be that John Paolucci is the plumber who was recently working on the baseboard and cut himself on a steel fin, coincidentally just below the window where the perpetrator entered, . Then the crime scene unit collected a blood swab from that location that produced the DNA hit. In these examples John Paolucci had legitimate access to the scene, but does that mean he isn’t the perpetrator? Investigators have a difficult job ahead of them.
Prior to uploading DNA into the CODIS databases, CODIS managers have to make certain that attempts to obtain DNA exemplars (samples) from all persons with legitimate access to the scene were made for elimination purposes. In many agencies it is the duty of the investigating detective to make all efforts to collect DNA exemplars from persons with legitimate access – but wait! People don’t want to stick swabs in their mouths and give big brother something as personal as their DNA. What if the computer comes up with that illegitimate child I may have fathered in Daytona, spring break 2004?
It can be very difficult to put people at ease when requesting that they provide a DNA exemplar, but the investigator needs to explain how much worse things will be if they refuse. They need to know that since they are regularly in this location, they have no doubt deposited some form of DNA there. If swabs and other DNA evidence collected from the scene are analyzed, the profile developed may be theirs. If they refuse to provide an exemplar then they will give the defense a significant loophole: “That’s not my client’s DNA!” If they provide an exemplar then the presence of this DNA that is foreign to the perpetrator is explained.
When the reason for not providing an exemplar is a fear that they will end up in a database, then the investigator has to explain to them that all probative and unknown DNA profiles developed from crime scene evidence are uploaded into the CODIS databases. In the event that the profile developed is theirs, and they are not eliminated, their DNA goes into CODIS. When their DNA is submitted for elimination purposes, it remains in that particular case file and is only compared to other profiles developed in that case and NOT uploaded. So refusing to provide a DNA exemplar makes it MORE likely their DNA will go into CODIS.
I have seen remarkable success when “Abandonment DNA” collected from suspects matches DNA collected at crime scenes. There essentially two means for collecting an abandonment DNA exemplar: A “ruse” and “covert surveillance” The set-up is your call, but let me just give some pointers on how to minimize contamination risks.
Covert surveillance can be very challenging. The investigator must follow his suspect and wait for him to abandon an item onto which he has deposited his DNA. This could include cigarette butts, drinking containers, eating utensils and items of this nature. The investigator MUST be certain that the item collected is in fact the same item that the suspect discarded. In other words, if the subject discards a cigarette butt on a street corner and there are several cigarette butts on the ground when the investigator goes to collect it, then this is a “Do-over” if he or she is not sure which one it is. Likewise if an item is thrown into the trash and commingles with other items that were previously deposited in that receptacle, a mixture may have occurred and efforts to collect the suspect’s DNA must continue. I recommend you work in a team where one detective follows the suspect and then maintains eye contact with the item and notifies his partner who comes to collect it. Again, the wrong person’s DNA will damage your case.
A ruse is when an investigator has his or her subject come in for an interview or some other excuse for an in person meeting, and hopefully the subject leaves some DNA behind. It is highly recommended that the room be prepared for this endeavor. Put a new liner in the trash can, clean the table with 10% bleach, have a new disposable ash tray on the table. When a subject leaves a cup, can or bottle behind that still contains liquid the best way to prepare that item for packaging without jeopardizing the DNA on the rim is to poke a hole in the bottom with a clean, sharp object and let the liquid drain from the bottom.
Cigarettes and gum are other consumables that may appeal to your subject. With these items, it’s best to toss the whole pack to your subject and have him remove the item to be consumed. When you think about removing a cigarette from a pack, you grab the filter with your fingers. Depending on what type of “shedder” you are, you may be creating a mixture. If the subject touches the filter of the cigarette he is going to smoke, it’s still in play. If you think you contaminated the evidence and you’re not likely to get another shot at this suspect, submit it with a sample of your DNA – as you tell your victims, it only stays in that case file. I’ll address concerns about cops’ DNA in a future article.
In both abandonment scenarios, always prepare your packaging ahead of time with the requisite case information. Once the item is in the packaging it is more difficult to write on and there is a risk of the writing instrument poking through the bag, contaminating or creating the potential for destruction of the DNA on the item. Check with your CODIS manager to see how low the threshold is to declare someone a “suspect”. You may be pleasantly surprised and have a gateway into the local DNA index system where he or she can be compared to the unknown crime scene samples therein.
