Recently, a string of church burglaries were happening in Florida. One of the scenes had a latent print left on a tile surface and a screwdriver left behind. The print was on a porous surface, which did not allow for the print to be lifted for analysis. Instead the CSI's took a DNA swab of the print and swabbed the screwdriver.
The used PCR to amplify the DNA to find a possible match. It did in fact come back to a suspect in the FBI database.
So what makes touch DNA a good source to use? Humans naturally sweat when under pressure (like committing a crime), which causes for DNA to be left behind on everything that is touched. When a sample of touch DNA is obtained, only about 30 cells are needed to do adequate analysis; this is a tiny number compared to the about 1 million cells that humans lose daily. From there, analysis is done on about 13 DNA locations that are quite specific to every human. This usually gives an accurate enough match of 1 suspect versus 330 million people.
Here is my question: If you had both a good latent print and good touch DNA, which would you rather do analysis on? Also, which do you think will give a stronger positive match?
Article in ABC News
I would rather do DNA analysis from touch DNA rather than develop the latent print. The latent print match to an inked print is at the discretion of the fingerprint analyst, there is no set number of level two detail matches, the minutia, needed to call a fingerprint a match. There is limited possiblity of human error when dealing with DNA. It also takes less time! Looking at ten print cards and making comparisons can take a while, whereas the DNA match is done through a database! TV makes fingerprint identification look super easy, scan, search, match! It doesn't actually work that way.
ReplyDeleteI agree. I worked with latent print identification this summer, and it was tough! It was also very time consuming like you said.
DeleteI would want to use the DNA analysis. It seems to me that analyzing the DNA would be easier and a more accurate way of identifying the person. Just like in the article, even if there is a print doesn't mean it will always be obtainable. DNA just seems like the right way to go.
ReplyDeleteI agree. Prints aren't always guaranteed to get a match.
DeleteThank you, Lindsay! So many people are under the impression that fingerprint matching always works, and it doesn't. To me, using DNA to identify a culprit is the obvious better choice. Now you mention that the sweat holds the lost DNA. That actually could make things easier in the future, as even criminals smart enough to use gloves can sweat from an uncovered part of their body onto potential evidence.
ReplyDeleteNot only does latent prints not always work, sometimes you've had to waste many hours to figure out that it doesn't work.
DeleteAn uncovered part of their body like their face that they're not even realizing is sweating and dripping off onto something!
Fingerprints on Porous surfaces like paper, cardboards and whatnot are easily identified using a chemical substance called Ninhydrin. (the fingerprint should appear violet in color). Touch DNA could be used as an alternative. Latent prints and touch DNA are both confirmatory tests. My choice will be which one is easier to conduct/lift? which one cost more? As a forensic scientist, I know that DNA and PCR amplification is a tiresome process (we all know that from Biology lab). I personally conducted the Ninhydrin test for lifting latent prints and it took me 5 mins (spray the substance, apply some heat and BAM you got all the print)....
ReplyDeleteI like your reasoning as to why you would choose latent prints. Then it would just be a matter of which of the two results is more likely to give a positive match?
DeleteAlthough latent prints have been proven to be a good method for identifying suspects, there has been times that it was wrong. One case in particular to my knowledge incorrectly identified a man because his fingerprints closely resembled someone else's. In my opinion, if both are available, I would chose the touch DNA since it seems a little more concrete.
ReplyDeleteI agree. But then again, DNA could incorrectly match the wrong identical twin whereas each twin would have separate fingerprints even if they do have identical DNA.
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