|Posted on Tuesday, March 02, 2004 - 07:02 am: ||
Like latent prints on skin, surfaces sprayed with WD40-like oils may give up most of their identifiable latent prints by simple visual examination. If the thieves left prints deposited in dirt, a thin film of oily spray may not necessarily obliterate them. It may even darken them and improve contrast in some circumstances. If the thieves touch the surfaces after spraying, the oily coating may collect latent prints deposited in dirt even better than a clean surface. Dusting with powder before photography would probably obliterate such impressions.
The next exam method I would recommend would be RUVIS, in that it causes oily films to appear as opaque instead of transparent. The surfaces would look as if they were spray painted with shiny black paint. The viscosity of the oily film may or may not interfere with latent prints under many circumstances, but some areas should exhibit really nice LPs. Some latent prints under the oil may even be visible when latent print deposits interfere with the surface tension of the oily film.
Do you know if they have tried SPR? There should be a "chance" for enough differentiation between latent prints and the oily coating, especially if the surface was touched after spraying. Even if it doesn't work for them at every crime scene, I would anticipate that it is worthwhile.
As a last resort, if the evidence was something small like a knife, I would recommend trying the Japanese "wet cyano" technique of dissolving a small amount of cyanoacrylate in petroleum ether and then dipping the evidence. As the ether dries, the prints appear developed in cyano. I do not recommend trying this on an entire vehicle.
Observe all applicable safety recommendations, of course.
|Posted on Tuesday, March 02, 2004 - 06:52 am: ||
Initially received from Jeri Eaton, who received the query from elsewhere:
We are getting dumped stolen cars sprayed all over with what smells like WD40. Presumably they are doing this to prevent us from lifting prints... Any ideas on getting around this?