Feb 14 2019
Which Came First – the Helix or the Whorl?
One of the earliest and longest lasting means of forensic identification is fingerprinting. Frequently, DNA is now considered the golden standard in the courtroom for forensic identification and is often called genetic fingerprinting. But what happens when these two means of identification cross paths? Contrary to what TV shows will have you believe, one forensic scientist does not specialize in every element of forensic analysis. In 2015, while working on a cold case for a television show, my forensics world came full circle. DNA Labs International was to process the DNA for the case while Ron Smith & Associates would be processing the fingerprints. I had heard Ron Smith speak at a forensic seminar at sea as a student nearly a decade earlier. It’s at this time in 2015 that I first spoke to RS&A’s technical manager Matt Marvin. Three years later he is still my go to fingerprint expert when it comes to DNA cases that also need printing.
Written by: Rachel Oefelein and Matt Marvin
The First Case (2015)
Rachel H Oefelein: Blood-soaked newspapers were believed to have the fingerprints of the suspect on them. The papers were sent to Matt who processed for prints and then marked them so that we could follow by consuming the prints for DNA analysis.
Matt Marvin: We received 11 pieces of newspaper, three paper bags, and one piece of manila paper. We processed the items with 1,2-indanedione complexed with zinc chloride, followed by laser examination with a 532 nm laser. It’s important to note that this specific formula adds the zinc chloride in a working solution rather than as a second step. As a working solution, the zinc chloride is in lower concentration (0.00004 g/mL) vs the higher concentration of applying zinc as a second step (0.04 g/mL); and the higher concentration does not develop latent prints any better. We obtained ridge detail off of multiple items and photographed the ridge detail. We then circled the areas of ridge detail with a clean fine point sharpie so that DNA Labs International could extract the ridge detail, as the ridges were not visible without the use of a laser.
RHO: The newspapers were returned to us and we were able to obtain a DNA profile suitable for comparison.
The Serial Killer (2016)
RHO: While working an ongoing serial killer case our laboratory received items of evidence with writing from the suspect. After consulting with Matt, and examining photos of the evidence, we decided to sample the areas without writing for DNA first and then sent the items to Matt for printing. If prints were found, he would preserve them with photography and return the evidence to us to consume the prints for DNA.
MM: This case consisted of a mix of paper and plastic items. After we received the items from DNA Labs International, we used the same process as we did on the 2015 case for the paper items. For the plastic items, we fumed them with cyanoacrylate ester, followed by a Rhodamine 6G dye stain, then visualized the prints with a 532 nm laser. It’s important to note that Rhodamine 6G has two formulas; one with a distilled water solvent and the other with an alcohol solvent. We specifically chose the alcohol formula so as to avoid any potential contamination with water. We developed ridge detail on all the items and circled thirty-three areas of ridge detail for further examination by DNA Labs International.
RHO: A print from the paper item was collected and consumed for DNA analysis. A mixture of two individuals was obtained and the profile was suitable for comparison utilizing STRmix™, a probabilistic genotyping computer software program that helps analyze complex DNA mixtures.
Cold Case with Prints (2018)
RHO: In an ideal world, all cases would be tested in accordance with a testing plan pre-arranged by all the necessary examiners. However, with cold cases and evidence that has already been tested we can’t be so lucky. In 2018, our laboratory was contacted about an item of incoming evidence that had been previously processed with a type of fingerprinting we hadn’t yet come across; naturally, we reached out to Matt to get suggestions.
MM: Oh boy. These items were processed with vacuum metal deposition (VMD – sounds like a disease). This is an old process that was hugely expensive to run. The chambers alone were so expensive that they were sparsely used in the United States, but there were a few chambers in Canada. Within the last three years, there has been a resurgence of this technology. The chambers have been redesigned, are smaller and cheaper. First of all, how it works: In vacuum metal deposition, we are going to put items in a chamber, create a vacuum inside the chamber, then evaporate gold and allow it to land across the entire surface of the item. Then, we evaporate zinc and allow it to land across the entire surface of the item in a thicker coat than we did with the gold. An alternative to this is to do a single application with silver. There is at least one major concern as we look at DNA, outside of any concerns about a dirty chamber, and that is the ions. Silver: Ag (1+), Gold: Au (1+), but the thickest coating across the entire surface is Zinc (2+). As a DNA analyst, be aware of any conflict with your planned extraction method that is going to perform poorly with a significant amount of metal ions.
RHO: Three samples were taken from this item; one avoiding the previous metal deposition staining and two samples where we sampled right through the staining. All three samples produced profiles suitable for comparison.
MM: Latent print processes can pose some specific difficulties for subsequent DNA examinations including metal ions, processes that are catalyzed by exposure to UV light, and reagents that are mixed or rinsed with tap water. There are over fifty chemical processes that are used to develop latent prints in laboratories all over the world, and multiple chemical formulas for many of these processes. In addition, any time RS&A works a case that will include DNA examinations, we thoroughly clean all our work areas, instruments, equipment, sharpies, etc. with bleach and ethanol, followed by a dry time. Latent print examiners need to work with their DNA analysts to understand extraction methods and potential sources of contamination in order to choose the best processes for the successful development of latent prints while simultaneously preserving the DNA.
RHO: As diverse as the world of DNA analysis can be, so can fingerprinting. We commonly come across old and new methods of fingerprinting that we weren’t previously used to processing. As a large DNA laboratory, we have many extraction tools at our disposal and different methods may be better equipped to handle different items of evidence previously fingerprinted depending on the method used. Additionally, a print that may not meet the criteria for a print comparison can serve as a great source of DNA. As examiners we often wish, especially with large items, if only I knew where the suspect, victim or person of interest touched the item. With printing we have the answer! It’s always best to consult and rely on our colleagues in the field of forensics so we are giving the evidence the best opportunity to reveal it’s truth, to speak for the victims that no longer can and to provide resolution to the families of those lost that are so desperately awaiting an answer.
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