Myth of Fingerprints

“I’ve seen them all and, man, they’re all the same”. OK, perhaps not quite all the same as Paul Simon says, but there are enough similarities to bring doubt on the surety of “a match”. TV and movies make it all seem so simple. Throw the latent print found at the scene or on the murder weapon into a computer and out pops the name (and often a picture) of the guilty party.

This was brought up to me a few years ago when a juror asked if we had fingerprinted the weapon that caused the death in a death by suicide to prove that the individual had indeed shot himself. That and some recent reading brought out a couple of tidbits that I thought I would share. 

Fingerprint identification happens when the arches, whorls, and loops present in a fingerprint are compared to some prints that are on record in a database somewhere or compared to a set taken from a specific individual. The comparison process finds parts that seem distinctive in the found print and those bits are compared to the set of possible fingerprints looking for similarities. So the second limiting factor in print ID is that you have to have a print of a known individual to compare with. That does not always exist, although it always seems to on TV. 

The first limiting factor is getting that latent print, latent print means one left behind to be found. The thing to know here is that the average latent print is only about 20% of a fingerprint, severely limiting the amount of the print information available for comparison. In the case of a gun trigger, the maximum amount of a print that could be found (not even considering that gunmetal is a poor surface to recover a print from) would be well less than that 20%. Definitely not enough data points for any real comparison.

Even if you have a full print, is this comparison thing an exact science as we are led to believe? Consider that a study done a few years ago in seasoned fingerprint examiners (I have lost the exact reference) showed as much as a 1 in 5 misidentification rate. Many times there are similarities enough to fool the most seasoned of investigators into making an incorrect finding, let alone the initial fingerprint screen by computer comparing thousands upon thousands of prints. It is not an exact science. The best that can be truthfully said is that there is a certain probability of certainty that this print matches a given individual’s. There is always the possibility of at least very similar prints being present in multiple individuals.

Do we really know that people with identical fingerprints don’t exist? In one episode of the Sopranos (don’t you miss the Sopranos?), Christopher waxed poetic on just this issue. His point was that without actually comparing everyone’s fingerprints in the entire world, alive and dead, you can never know for sure that there are no identical fingerprints. Keep in mind that Nancy Knight of the National Center of Atmospheric Research found 2 identical snowflakes during a snowstorm in Wisconsin a few years ago. If the myth of no identical snowflakes existing has been busted, who are we to say that the same is not true of fingerprints?

Cocaine in a Poly-substance Death

I am back to blogging here. I missed this site, but, interestingly, even when I wasn’t posting I still had something like 80 visits per day on average. It may be a lazy re-start, but I am going to begin by elevating a comment for the "Cocaine and Death" post. (Even when I wasn’t posting here comments have been posting and I have been answering questions)

A comment by Anonymous:

Thank you in advance for any answers you may be able to give. My boyfriend was alive at 8am on Friday and found dead at 5pm on Saturday. He was a very depressed drug addict that had been self professed clean for 9 months. The date of the autopsy was Monday morning at 8am which is 39 hours after he was found. My first question is are the toxicology numbers based off blood tests done @ time of autopsy or was blood taken @ crime scene? What I want to know is...when it shows a certain number for cocaine and benzoylecgonine in his blood, has some of it had time to leave his blood before the count was taken?

It shows results from blood test as follows: Ethanol 0.035 g/100mL Carisoprodol 9.1 ug/mL Meprobamate 4.4 ug/mL Cocaine 65 ng/mL Benzoylecgonine: Present not quantified Zolpidem: Present not quantified The supplemental report on liver tissue specimen showed Zolpidem 1700 ng/g Another supplemental report taken from chest blood to show Zolpidem 650 ng/mL

The autopsy ruled diagnosis as
1. Multiple drug toxicity a. circumstantial evidence b. diffuse visceral congestion c. pulmonary edema and congestion d. froth & aspirated content in upper and lower airways e. postmortem blood toxicology: Multiple drugs present. Zolpidem is in toxic range
2. No significant trauma
3. Early postmortem decompositional changes.
Manner of death: Accident
In the report it shows he had greenish skin coloration in several places as well as marbling apparent over left side of trunk and left thigh.

My questions are 1. when they talk about decompositional changes such as marbling, are they going by time of autopsy or when found at crime scene? Trying to find time of death 2. when they talk about the levels of each drug in the system are they talking about blood taken at crime scene or from autopsy 3 days later? Did drugs have time to leave his system and alter numbers? He had been depressed for a week and threatened suicide. So many drugs in his system including the cocaine and "toxic levels" of ambien yet ruled an accident...why? When did he last use cocaine and how much? Does this look like suicide to you? And what time would you put his death? I thank you so much for taking the time to read this. I appreciate any answers you may be able to provide.
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There is a lot of great stuff in this comment. First of note is the classic autopsy findings of an overdose death. “Froth”, also referred to as “Purge” or purge fluid, was found in the airways, classic. Vascular congestion was present in the lungs and other organs. Aspirated material was also noted in his airways. This combination of autopsy findings scream overdose. Considering the lab results, the zolpidem/Ambien level found is definitely in the toxic range. While not at toxic levels, it is important to not ignore all of the other substances obviously ingested, most notably a muscle relaxant and alcohol. Certainly the cocaine should not be ignored as well. It would have been most appropriate to call this individual’s death as due to poly-substance ingestion.

As I replied to Ms Anonymous: “I would agree with your feeling that the mix of drugs makes it likely that this was a death by suicide. Particularly in view of your relating that he had been depressed and threatening suicide recently. Although, people don’t use cocaine for suicide, as a rule, the others drugs with the Ambien at that level would have me to call this a suicide. Some investigators/coroners are hesitant to call a suicide, even when it stares them in the face. They, too, are inhibited by the possible stigma and the possible reaction of family and friends to suicide being listed as a manner of death. That is unfortunate and a disservice to all. We need to move beyond the stigma and approach suicide head on or we will never be able to make treatment available to those in need.”

The body also had early signs of decomposition present at autopsy. This may seem a bit early for it to begin, but cocaine and other drug overdoses, as well as death in hot surroundings (not known in this case), can speed the decomposition process.

I also commented: “The cocaine level would seem to point to a draw shortly after the body was found. Cocaine does metabolize in the body after death, via red blood cell enzymes. The level of cocaine in his blood, and not just the metabolite benzoylecgonine, would tell us that he died within a couple short hours after use (anything more defined would be guess). It is a little trickier to known when he died without further information regarding rigor, livor, etc, but likely not all that long before being found. Also, there is no way to back calculate to tell the amount of cocaine used.”

Keep those questions coming in. I am honored to help folks find the answers to questions that they can’t seem to get answered elsewhere, apparently including where these deaths have been investigated. I look forward to our ongoing discussions and being able to share information with you, my readers.