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New Insight into the Chemical Improvement
of Shoeprints and Fingerprints Placed
with Blood on Non-Porous Surfaces

Theo Velders


Shoe prints and finger prints placed in blood on non-porous substrates are usually treated with chemical means to achieve a better contrast of the blood traces on the carrier material. The subject of this research was to explore the possibilities to improve visualization of blood traces, after they were detected with Luminol, by exposing them to other chemicals, such as Leuco Crystal Violet (LCV), Acid Yellow 7 and/or Hungarian Red.

This research led to some very interesting results, which shows that LCV appears to be a less suitable chemical to improve this visibility on non-porous substrates.

Looking for answers

In the course of time I found myself confronted with a number of questions about how to improve shoeprints and fingerprints in blood. These questions arose because I learned about the increased use of Luminol for detecting and/or visualising blood traces in relation with DNA research. For this, the use of Leuco Crystal Violet (LCV) reagent to process and/or enhance traces found on non-porous materials has increased too. The reason for this is that LCV is easy to use. It can be applied without first fixing the blood trace. The formula of LCV already incorporates the fixing agent 5-sulfosalicylic acid. Also, LCV is colorless and only assumes a color once it reacts with blood. To prevent discoloring of the surface it is advised to rinse afterwards, at which point the visualized trace must be photographed immediately. Online searches into this issue of the chemical improvement of shoeprints and fingerprints in blood result in reports where the LCV reagent is recommended as a very good enhancement product for fingerprints and shoeprints in blood on non-porous surfaces.

See for example the traces on Photos 1 and 2. I will further discuss the traces shown in Photo 1 and 2 later in this article.

What did not become entirely clear was how one had arrived at the conclusion that LCV is a good enhancement reagent for shoeprints and fingerprints in blood on non-porous surfaces. I suspect that this conclusion was fed by the simplicity using the product.

My questions therefore were:

  • In what way did one establish that a blood trace treated with LCV has shown all the latent information that may have been present in a trace?

  • Did one subsequently treat the blood trace treated with LVC with another chemical product, in order to verify whether all the latent information in the trace had been developed?

It probably has not been done, as it was not done in the CHEMZIS research: once a blood trace was treated with a chemical reagent or staining solution, the same trace was not used again to look for a possible enhancement with a different reagent or staining solution.

In the past I made this same mistake myself and failed to look for a possible enhancement of a blood trace already treated, even though this was standard procedure with latent fingerprints, using, for instance 5-MTN after having used DFO. I never thought that this would also be possible with blood traces.

< read the complete article and view example photographs >

Article submitted by the author

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The beginning of this manual is a list of processes and procedures for different surface types. Also included are processing sequences that specifically involve prints that are left in blood. Following these lists are details for each process that is currently implemented in the Latent Print Unit (LPU) of the Federal Bureau of Investigation (FBI) Laboratory.

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