Now, we use powder in the FBI only on objects which have a hard, smooth, nonabsorbent finish, such as glass, tile, various types of highly polished metals and the like.
In the FBI we do not use powder on paper, cardboard, unfinished wood, or various types of cloth. The reason is that the materials are absorbent. Accordingly, when any finger which has on it perspiration or sweat comes in contact with an absorbent material, the print starts to become absorbed into the surface. Accordingly,. when an effort is made to develop latent prints by the use of a powder, if the surface is dry, the powder will not adhere.
On the other hand, where the surface is a hard and smooth object, with a nonabsorbent material, the perspiration or sweat which may have some oil in it at that time may remain there as moisture. Accordingly, when the dry powder is brushed across it, the moisture in the print will retain the powder giving an outline of the impression itself.
These powders come in various colors. We utilize a black and a gray. The black powder is used on objects which are white or light to give a resulting contrast of a black print on a white background. We use the gray powder on objects which are black or dark in order to give you a resulting contrast of a white print on a dark or black background.

Mr. Eisenberg.

Now, Mr. Latona, how did you proceed to conduct your examination for fingerprints on this object?

Mr. Latona.

Well, an effort was made to remove as much of the powder as possible. And then this was subjected to what is known as the iodine-fuming method, which simply means flowing iodine fumes, which are developed by what is known as an iodine-fuming gun--it is a very simple affair, in which there are a couple of tubes attached to each other, having in one of them iodine crystals. And by simply blowing through one end, you get iodine fumes.
The iodine fumes are brought in as close contact to the surface as possible And if there are any prints which contain certain fatty material or protein material, the iodine fumes simply discolor it to a sort of brownish color. And of course such prints as are developed are photographed for record purposes.
That was done in this case here, but no latent prints were developed.
The next step then was to try an additional method, by chemicals. This was subsequently processed by a 3-percent solution of silver nitrate. The processing with silver nitrate resulted in developing two latent prints. One is what we call a latent palmprint, and the other is what we call a latent fingerprint.

Mr. Eisenberg.

Can you briefly explain the action of the silver nitrate?

Mr. Latona.

Silver nitrate solution in itself is colorless, and it reacts with the sodium chloride, which is ordinary salt which is found in the perspiration or sweat which is exuded by the sweat pores.
This material covers the fingers. When it touches a surface such as an absorbent material, like paper, it leaves an outline on the paper.
When this salt material, which is left by the fingers on the paper, is immersed in the silver nitrate solution, there is a combining, an immediate combining of--the elements themselves will break down, and they recombine into silver chloride and sodium nitrate. We know that silver is sensitive to light. So that material, after it has been treated with the silver nitrate solution, is placed under a strong light. We utilize a carbon arc lamp, which has considerable ultraviolet light in it. And it will immediately start to discolor the specimen. Wherever there is any salt material, it will discolor it, much more so than the rest of the
object, and show exactly where the latent prints have been developed. It is simply a reaction of the silver nitrate with the sodium chloride.
That is all it is.

Mr. Eisenberg.

Do you frequently find that the silver nitrate develops a print in a paper object which the iodine fuming cannot develop?

Mr. Latona.

Yes; I would say that is true, considerably so. We have more success with silver nitrate than we do with the iodine fumes.
The reason we use both is because of the fact that this material which is exuded by the fingers may fall into one of two main types--protein material and salt material. The iodine fumes will develop protein material. Silver nitrate will develop the salt material.

« Previous | Next »

Found a Typo?

Click here

Last Update: Wed, 3 Aug 2016 21:56:36 CET