Thursday, May 03, 2007

Powder and water aren't always enemies

As a part of ongoing training in crime scene investigation, our Lab has developed a training and familiarization exercise that is conducted every week. It consists entirely of trying to find items that seem unlikely for processing and then finding ways to process them. By doing this, we learn first-hand what process works best for specific items and figure out ways to collect evidence from things that most other people wouldn’t even try. Recently, we experimented with some plastic bubble wrap that had been lying on a shelf in the work bay for months.

Several methods were attempted consisting of basic powder, magnetic powder, fluorescent powder, iodine fuming, ninhydrin, cyanoacrylate and dye stains. We even played with Liquinox and gentian violet. Nothing worked very well but the most promising method seemed to be magnetic powder. We could see some ridge detail but most of it was obscured because the powder was also sticking to the background behind the print. These photographs were taken with rear illumination using a light box.

Inv. Nancy Peacock decided to try a few things that weren’t in the standard arsenal of crime scene processing. Since mag powder performed slightly better than the other methods, she modified the application. After fuming a piece of bubble wrap with cyanoacrylate, she applied magnetic powder. But then she rinsed off the plastic with plain water. What she discovered was that the background scatter rinsed off and the latent print still remained. The clarification of the print was astounding. She tried a few more experiments and made a slight improvement to the rinse by adding Photo-Flo.

One important point I would like to add to this technique is to be careful of reverse prints. We have repeated this experiment several times on different items and have found that the prints will be reversed in some cases but not in others. We are still trying to identify the exact properties of this method to determine why it is not consistent in regards to print reversal. The print on the left is a reversed print which is indicated by the lighter color of the ridges over the background color rather than darker color ridges over the background.

The next time you use mag powder and end up with a tremendous black mess, you might want to give this idea a try. More than likely, you will end up with a viable print. If that doesn’t work, try something that no one has ever suggested to you before. You might just end up with a new technique that you will find yourself using for the rest of your career.