CLPEX Chat Board

Hi All,
I am trying to find references that discuss the effect plastic evidence bags/envelopes have on latent prints. I was taught that plastic creates a static charge, similar to rubbing an inflated balloon on hair, to effectively "lift" the print off of the item of evidence and into oblivion. However, I cannot find any scientific references to this phenomenon. Ernie Hamm's index did not bring me luck this time. Thank you!

I have never heard of this problem. I have successfully obtained latent prints on papers and non-porous items stored in plastic bags, sometimes stored for weeks in plastic bags. It could be that the contact of the plastic bag against the non-porous items caused the latent print to rub off just as if you rubbed your own finger across the latent print, but the same could be true for a non-porous item in a paper bag. I don't believe it has anything to do with static electricity.

And, because the latent print is "absorbed" into paper evidence, rubbing isn't too much of an issue.

While plastic is not my favorite packaing material, I have still recovered latent prints on items packaged in plastic.

Kathy

I imagine all of us have succesfully processed evidence that is stored in plastic. I have been successful most recently with a cold case in which the evidence was stored for fifteen years in plastic bags. What I am referring to is a specific phenomenon of static electric charge reacting with charged particles (eg- amino acids from degraded proteins carrying a charge).

Specifically, I am referring to a case in which I have a few dozen fraudulent checks. Some were packaged in plastic check envelopes before being put in plastic bags. Others were loose in manila envelopes. I was extremely successful in developing multiple latents on each of the checks in the manila envelopes. However, I was not successful in developing a single print with any kind of clear ridge detail from the checks in the plastic sleeves. Ergo, I am looking for an explanation to explain these results. Any thoughts?

This is off the topic but still an interesting case of disappearing prints. A few years back I had to take over a case that already had an examiner and a verifier (I don't remember the reason I was taking it over). Part of the evidence was processed with VMD. The developed latents were photographed and lifted.

On the back side of one of the lift cards was identification information and the examiner and verifier's signatures. On the other side of the lift card, where you'd normally see the latents, there was only a piece of tape (no latents). I asked the original examiner and the verifier about it and the only explanation they had was, "It must have faded".

Has anyone else ever heard of this happening or do you think I'm just gullible?

From the geletin-rubber lifter info from Lightning:
http://www.redwop.com/technotes.asp?ID=92

"Lifted dusted prints will fade, and ultimately disappear in time. Fading will be noticeable after days or weeks, depending on the storage temperature (the lower-the better). Prints developed with silver powders, on the other hand, are known to have been stored for several years without apparent fading. It is recommended, though, to photograph prints as soon as possible."

Kathy, can you elaborate?

The information in that Technical Note was developed by the manufacturers, BVDA in Holland. It is my understanding that the gelatin in the lifter is a food preservative and there can be a reaction that can cause latent prints to fade over time, the same with dusty shoeprints. The reaction is in the gelatin, not the plastic. And, from their research, the silver powder didn't seem to be adversely effected as much as other powders.

Getting back to the papers in the plastic sleeve issue, Hillary's example would seem to warrant further study. While I have developed latent prints on checks that were in plastic sleeves and not in paper envelopes, they have been individual cases that cannot be correlated as in Hillary's example. A question for Hillary - which formula of Ninhydrin were you using? Might that something to do with the situation also?

As to Michele's question of fading latent prints developed with VMD, I don't have any experience with that process. Hopefully, someone who does will be able to comment.

Kathy

Also a great hypothesis! I hadn't considered the formulation of Nin to be a problem. I use the HFE 7100 solvent. I love the stuff. It has always provided the best results.

Perhaps this issue is an interesting masters thesis?

Hello,

I have another hypothesis -

Paper and other porous surfaces contain moisture. If they are placed in plastic bags, over time the mositure can evaporate or migrate from their original position in the paper and cause the fingerprint to smudge.

When placed in a manilla folder, the evidence is able to "breathe" to an extent, so either the evaporated mositure can escape, or the manilla folder will absorb it and keep it away from the prints.

This is why I think the SOPs in Australia specify that paper samples be placed in paper envelopes. Perhaps Les can confirm this?

Cheers,
Shaheen