Enhancement of Latent Prints in Blood

This article is the 12th and final article in a comprehensive series of twelve articles on latent print development techniques written by Pat A. Wertheim. Save these issues of Minutiæ in a binder to compile a manual of fingerprint development techniques.

Many of the techniques for developing "normal" latent prints do not work suitably on prints in which a significant portion of the latent print residue is blood or blood serum. Therefore, in violent crime scenes or on evidence where blood is present, many examiners choose to use a method specifically formulated to detect bloody prints.

First of all, a very careful visual examination for latent prints must be made using oblique lighting (shining a flashlight flat across the surface), then direct reflected lighting (looking for prints in the glare of reflected light on the surface). Any prints visible under either of these methods should be photographed prior to any development methods.

Next, a fluorescent examination of the surface may be performed for prints with inherent luminescence, followed by photography if prints are found.

For blood-based latent prints which are not visible and cannot be photographed without chemical development, however, several chemical techniques are available.

First of all, Ninhydrin may be applied. Ninhydrin, of course, is an amino acid reagent which will turn the print dark purple. Ninhydrin is more often used on porous surfaces for normal prints. While it does react with blood components, it is not considered the method of choice for blood prints.

More commonly, amido black, a protein dye staining method, is used for bloody prints. For most nonporous surfaces, amido black is prepared in methanol based solutions. A pre-wash of methanol is used to "fix" the print. Then the solution with amido black dye is applied, either by immersing small items or by washing the solution gently over larger items. Finally, rinse solutions are used to clear the background.

Amido black may also be used in aqueous (water based) solutions. While ridge detail generally does not develop as crisply with the aqueous solutions, this option has the advantage of being less hazardous than the methanol solutions and may be used over large areas at scenes of crimes.

A new product on the market is a pre-mixed, one step amido black solution which combines the "fixer" and "developer." While chemical purists may down-play the idea of such a combination solution, the layperson who is uncomfortable with more sophisticated chemistry is still better off using a "one step" method than no method at all.

Another protein stain which works well on blood prints is Coomassie Blue. This method does not require a fixing step prior to staining, and is touted by some as being easier to use and producing less background staining than amido black. Another method mentioned by some is Crowle's staining solution.

It should be noted that any of these chemical methods will prevent subsequent DNA analysis or blood typing. Therefore, if blood typing or DNA are likely to be requested, sufficient samples should be collected for analysis prior to chemical processing for latent prints. If there is no blood present other than the print itself, then a decision must be made whether the latent print would be of more value, or whether the blood analysis is more important.

Some mention has been made outside the scientific literature of the use of luminol as a latent print development technique for bloody prints. However, luminol is used primarily as a technique for visualizing larger patterns of blood and is not recommended for development of fine detail such as that found in a latent fingerprint.

For more lengthy discussions of correct use of blood print development techniques, see the following sources:

1. Home Office Manual of Fingerprint Development Techniques, 2nd Edition, 1998.
2. Bodziak, William J., Footwear Impression Evidence, Elsevier Science Publishing Co., Inc., NY., 1990.
3. Norkus, Paul, and Kevin Noppinger, "New Reagent for the Enhancement of Blood Prints," Identification News, April, 1986, p. 5.
4. Lightning Powder Company Technical Note No. 1-2742, January, 1999.

This concludes the series on the chemical processing of latent prints written by Pat A. Wertheim. We really appreciate Pat's writing skills in bringing you these technical articles in the past several issues of Minutiæ. Now that he and his wife, Bonnie, are the owners of Forensic Identification Training Seminars, LLC, he won't have the time to write for us. However, keep looking in the Journal of Forensic Identification for more articles by this talented writer.