| Author | Message | ||
     Michelle Tait |
EVERYONE OUT THERE WHO CAN ANSWER MY QUESTION: Plse I need help. A 10 yrl old murder case yet unsolved. I believe because this small police Dept. are using a DNA profile which they are convinced belongs to the Murderer. Yet I know for a fact it is incomplete,& I believe contaminated. The dogs found Clothing from which they removed DNA they found in the snow,& did not handle properly.Now that they have this DNA profile it is the only investigative tool they are using,hence to killer.Is my concern valid? | ||
| Kasey Wertheim |
Chris, I would like to reiterate and build upon the information that Mr. or Ms. Tavernaro has given. I also agree that the best option would be collaboration between a DNA analyst and latent print examiner before processing. I also agree with the concept of magnetic powder, as the brush does not come in contact with the evidence itself; only the powder. If one were to use traditional black powder, the brush would become contaminated, as would the reservoir containing the powder, as the brush is 're-loaded.' I have experimented with and currently use a variety of percentage mixtures of black powder and magnetic powder. The magnetic powder makes an excellent carrier for the black powder and deposits it across the surface without contamination of a fingerprint brush. I use a mixture of approximately 50% black and magnetic, but I have mixtures with less black powder all the way down to pure magnetic powder. Different percentages are ideal for different surfaces. By utilizing percentage mixtures, you still get the effect of black powder without the cost involved in disposing of contaminated brushes. Of course, you cannot "clean" the print up using a camel hair brush or feather duster because of contamination, but a blast of compressed air from a distance (start out farther away and work inward) does nicely. And I'm sure you know not to blow across the print to remove excess powder, or YOU may end up on the suspect list!  Hope this info helps, and good luck! -Kasey Wertheim | ||
| R. L. Tavernaro |
Chris, I am a Latent Print Examiner with some experience coordinating with DNA analysts. A few suggestions that may mitigate potential DNA cross contamination as a result of prior latent print processing: 1. Whenever possible, a face to face coordination between the latent print examiner and DNA analyst with the evidence in their collective possesion, may extend the options for DNA swabbing prior to latent print examination. 2. When powder processing is called for, consideration should be given to the use of magna-powder techniques instead of normal brush applied powder techniques. Careful application of magna-powder to each item separately in a clean environment (clean butcher paper on a benchtop may serve as a clean "enough" environment in many cases), and subsequent disposal of excess powder, should serve to minimize cross-contamination that could occur from physical contact of a brush or re-use of powder. 3. If chemical processing is required, and it is determined that the specific process that is being used (including carrier constituents when applicable) will not interfere or seriously degrade subsequent DNA examination, the labware and examination environment need to be clean before & after the latent print examination. In addition, actual chemicals used should be applied in a single item exam, throwaway context. This may be a departure from normal practice. These are mostly just common sense laboratory practices, but perhaps you will find something worthwhile. If you research this question, I would be interested in the results. | ||
| Ernie Hamm |
See the article, "A Further Study to Investigate the Effect of Fingerprint Enhancement Techniques on the DNA Analysis of Bloodstains", Roux, Gill, Sutton and Lennard, in Journal of Forensic Identification, 49:4, July/August 1999. This involves research involving powders, fuming and chemical application. In brief, no technique has a serious adverse effect under certain conditions, but some techniques should be used judiciously. | ||
| Chris Sewell |
I do not work with latents directly, but I supervise DNA analysis in the Washington State Patrol Tacoma Crime Laboratory. Our section has been discussing lately the possibility of DNA cross-contamination due to latent print processing. This might ocurr while dusting from one item to another, particularly if the first item was a large DNA source, such as a heavily bloodstained article, and the next was something that may have only been handled. I was wondering if anyone in the field was aware of any studies (published or not) dealing with this as a realistic possibility, and what strategies might mitigate this. Sometimes DNA samples can be taken before processing an item for prints, but it is not always an (easy, or the best) option. Thank you. Chris Sewell WSP Tacoma Crime Lab csewell@wsp.wa.gov |
