Wednesday, March 28, 2007

Fingerprints from what???!

Sometimes, you run across items that you know were in the suspect’s hands that don’t lend themselves to traditional fingerprint processing techniques. Even with all of the possibilities like powder, ninhydrin, amido black, small particle reagent, Liquinox…just to name a few…there are still a few items that seem impossible. In case you can’t think of any, let me throw this one at you…


Fingerprint powder, even magnetic powder, sticks pretty evenly across the leaves and doesn’t enhance the latent prints. Ninhydrin turns the entire thing purple and wilts it almost instantly if you use an acetone base which changes the dimensions of the print. Amido black will only work if the print is bloody, and the glacial acetic acid/methanol combination isn’t friendly to vegetation. Small particle reagent sucks in general, but has the same problem on cabbage as powder. Liquinox and similar processes only work on skin cells embedded in glue.

Why would you want to process a cabbage? The same reason as processing anything else – because it may have the suspect’s prints that could identify the perpetrator. As a specific example, I worked a vandalism at a fruit and vegetable packing center, which usually doesn’t warrant a crime lab response, but there was nearly a quarter of a million dollars in damages to the forklifts and other heavy equipment that the suspects drove off of the end of the loading dock. I tried to get fingerprints from the machines, but they were too caked with oil and grime to get anything worthwhile. The suspects had thrown around a lot of fruit and vegetables, but most exploded on impact, like tomatoes. The only thing I had left to work with was cabbage. There were about a half a dozen heads of cabbage laying on the floor that the suspects had thrown, but didn't disintegrate like the other produce.

The solution is an often overlooked process – cyanoacrylate dye. Fume the item with superglue as you normally would and let it sit for a day to allow the superglue to set. Then either spray or dunk the item in a fluorescent dye stain. I prefer to use RAM which is a combination of Rhodamine, Ardrox, and MBD. Allow the dye to remain on the surface for about 30 seconds or so and then rinse it gently with distilled water. Using an alternate light source in a dark room, examine the item for latent prints. They will glow brightly and can easily be photographed with a scale for identification. I have used this technique successfully several times when nothing else seemed to work. It also was the key to solving a major crime at the packing center.