CLPEX Chat Board

I have a very faint fingerprint in blood on a smooth metal surface. The impression I can see has a lot of third level detail with no filling-in in the furrows. I have taken lots of photographs to document it.

Which processing technique should I use to enhance it? A dye protein stain (Hungarian Red/Amido Black) or LCV/DAB? What is the consensus on when to use a protein stain and when to use a reagent that reacts with hemoglobin?

Thanks for any help you can give me.

Alicia

Heme reagents are more sensitive and I find they almost always do a better job. I like LCV, but if the crime is very serious, I prefer to use tetrabethylbenzidine. It's a carcinogen; but I've used it sparingly (and with a great deal of precautions) for about twenty years and I've never found anything to do as well at developing sharp ridge detail in blood.

Must agree with benzidene being a great developer of blood prints...we have discontinued using it due to it being carcinogenic...not sure if we can still get hold of it even but it does give great results on blood prints.

I worked with it a few times in the early 90's and it yielded usable prints where the blood deposits where barely visible to the naked eye.

Let us know how things happen and what route you take.

Upon relooking at the posts this morning, I realized I mispelled the chemical. It's tetramethylbenzidine. Incidentally, o-Tolidine (another heme reagent) can be mixed the same way as TMB and gives great results. Its reaction results in a dark blue color, while TMB's reaction is green. The color of the item that the print is on should be the dictating factor as to which to use. I've spoken to some chemists who claim the o-Tolidine is safer; and I've spoken to other chemists who claimed TMB is safer.

Alicia, interestingly it was a chemist at your lab in Maine that originally gave me the TMB/o-Tolidine formula. It was about twenty years ago and I've long forgotton his name, but I remember he used the chemical to develop a bloody latent print on the leg of an elderly female who had been stabbed to death. She had been stabbed and the knife was left in her chest. When they placed her in the body bag, the handle of the knife acted like a pole in a tent and kept the bag from rubbing the bloody impression off of her leg. At autopsy, someone realized the blood stains on her leg looked like they could be fingers. The chemist, whose name I can't recall, was notified, made a batch of chemical (I think he chose o-Tolidine) and managed to obtain an identifiable latent print on her leg that subsequently was matched to the murderer. It was a hell of a job and I feel guilty for not remembering that chemists name.

Alicia,

Two things. 1) Personally, I like for shiny metals, Amido Black (as long as you appropriately fix the blood by heating the area or using a fixing solution prior to Amido Black to denature and fix the protein) [i.e. 5-sulphosalicylic acid in Methanol]. For darker surfaces, I was impressed with Amanda Atkins' (of the US Army Crime Lab) results using Acid Yellow 7. A quick google search will find her presentation with great images. But both are protein stains, and David makes a good point about the sensitivity of TMB and other heme reactors. I have less experience using TMB, so I defer to David on that one. Many agencies don't have a TMB protocol or validation in place, hence why Amido is good.

2) You may wish to use caution when relying on Level 3 Detail (L3D) in bloody impressions. I have done fairly extensive research with 1000's of blood prints and Ashbaugh in Q&Q FRA states a similar thing: blood creates many false artefacts, especially L3D. It is easy to imagine blood like taffy b/c of the cohesive properties and it tends have lots of false edges and features. I would highly recommend in general a very thorough analysis up front marking features that you trust and deem reliable before going on to do the comparison. This helps for cherry picking detail in the comparison and gives you a nice comfort zone for what you will and won't use in the comparison.

Just my 2 cents.

Alicia,

Heme reagents react with some metals (iron, copper, ...).

I'd go for a protein stain.

All the best,

Gerrit

Alicia,

From my experience I would use a great deal of caution using LCV on metallic/non-porous surfaces as the LCV reaction can often cause the blood contaminent to lift off the surface and be destroyed.

A colleague of mine had a very good result a couple of weeks ago using Acid Yellow on a metal towel rail, and it will be my choice of reagent based on his results. He also did a fine job of developing a bloody palm print (identified as the suspect)on the back of the deceased using Amido Black.

Good Luck.