T H E
D E T A I L
Monday, February 11, 2002
Good morning via the "Detail," a weekly e-mail newsletter that greets latent print examiners around the globe every Monday morning. The purpose of the Detail is to help keep you informed of the current state of affairs in the latent print community, to provide an avenue to circulate original fingerprint-related articles, and to announce important events as they happen in our field.
Last week, we examined a summary of the Government's memorandum in support of the motion for reconsideration of Judge Pollak's ruling against the admission of fingerprint testimony in US v. Plaza. If you didn't get a chance to read through that mouthful, check out the Detail Archives. Also, there has been some excellent discussion at the Onin forum on this topic, under "From FP Experts to FP Experts" Topic: "The science of fingerprints: an exact science?"
This week, we take a break from these events to look at a completely different subject; sequencing latent prints. Have you ever determined which overlapping print came first? Steve Howard gives insight on a case he had and the conclusion he reported. This should make for some interesting discussion!
It all started with a call I received from a prosecuting attorney in the middle of a homicide trial last year. The murder had occurred almost 20 years earlier in which the female victim had been sexually assaulted and murdered in a ravine. Related exhibits from the case had been received in my office at that time. I didn't join the Department until several years later but had occasion to examine a subsequent exhibit for fingerprints a couple of years ago, hence the reason for becoming involved in the case again.
As background, the submitting agency was another police dept. and they had developed three prints in very close proximity to one another on a glass vase found in the victim's apartment. The ident officer had developed and lifted the trio of prints, which had now been submitted in evidence. One of the prints had been identified (not to the accused or victim) and for some reason the remaining prints in the lift had never been accounted for. Naturally at trial, this became a big issue. Perhaps they belong to the REAL killer...?
That's when they called me. I was initially asked to compare these two unidentified prints against 13 individuals involved in the case. When I received the original exhibit and lift shortly thereafter, I confirmed the original identification, and upon analyzing the other two prints, deemed one of them to be unsuitable for ID purposes. The third (unidentified) print and the already identified one were in fact partially overlapped, albeit with sufficient detail in each print outside of the overlapped area to identify them both. I was able to exclude 12 of the 13 individuals as the source of the unidentified print including the accused. The remaining individual was in fact the victim and post mortem prints were of extremely poor quality for comparison.
Bear in mind that these prints were 20 years old by now. During my analysis of the f/pt lift , I could see that the print that had already been identified was noticeably 'darker' (or heavier) in appearance than the other. (darker = more recent, perhaps?) I tried to follow the ridges and resolve the detail in each print, but unfortunately, in some of the areas where the ridges of both prints dissected, they seemed to blend in with each other, forming an 'interwoven' cross-hatching pattern. I photographed the lifts and made enlargements of the overlapped area, analyzing every ridge in that cross-hatched area to see if I could see any ridge 'sitting on another'. I did observe two small parallel ridges on what would be a phalange area just below the first flexion crease that appeared to be sitting over another ridge flowing in a counter direction. However, this detail alone was, in my opinion, insufficient to make a determination for reasons I'll explain in a moment.
Next, a professional contact provided me with the only article on the subject he was aware of: Macroscopic Examination of Overlapping Latent Prints on Non-porous Items by John C. Saunders, JFI 43 (2) 1993.
In reading the article, the accompanying macroscopic photographs showed quite clearly which print was 'on top' as well as the explanation of how to distinguish between them. What I found interesting about that article though, was the fact that no mention was made about the volatility (or fluidity) of the medium that was being examined.
With latent prints being comprised mainly of water, or perhaps some foreign materials present on the fingers at deposition, I didn't think it would be unreasonable to assume that a 'merging' of the perspiration and/or materials from both prints might occur at some point over a period of time. If that's possible, could it not also be reasonable to assume that the ridges from the more recent print might actually 'appear' to recede into the other print, giving the false assumption that this was the 'older' print of the two?
Another important consideration was this possibility......what if the first print was composed primarily of sebaceous or oily material deposits, then a subsequent print from another source comprised of mainly perspiration is placed over top of the other one? Could the sebaceous deposits from the original print 'repel' the perspiration wherever the ridges crossed, effectively erasing that portion of the ridge, or the 'repelled' perspiration simply evaporating after a time. That would leave the portion of the ridges NOT in direct contact with the sebaceous portion intact, creating an impression (no pun intended) that the 'later' print now 'appears' to have been placed first. It was for this reason that my opinion had to be one of 'inconclusive' or indeterminable.
I discussed this with some of my colleagues and opinions concurred more of less with my own. As far as the trial was concerned, it was a few days later before I was called to testify to my findings and as things turned out, my 'inconclusive' opinion was important to securing the conviction, presumably because, based on the facts of the case, the timeline of when the 'identified' print was deposited, couldn't be argued.
My main conclusion from this case was this: Our instincts may initially tell us which print 'looks' the most recent, and hopefully, based on the detail we have to analyze, we can find enough information to support this conclusion based on a thorough analysis of the intersecting ridge flow. However, without knowing the specific composition of the latent prints, I wouldn't be comfortable making a positive determination for the reasons I mentioned and would recommend exercising caution when called upon to make this determination - just in case things may not be what they seem. Hopefully we'll see some follow-up research on this subject someday.
If this is an area you would be interested in doing research in, I would personally encourage you to gather past articles, get with Steve, and go for it!!
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Until next Monday morning, don't work too hard or too little.
Have a GREAT week!