Bloody Palm Print, Touch DNA, and a Paper Envelope: Sequencing Destructive Processing
A 29-year-old man is shot in an apartment stairwell. A metal magazine lies on concrete with a bloodstain shaped like a partial palm print and possible touch DNA on the grip. A patent bloody footwear print is on the door. A latent print is suspected on a paper envelope on the kitchen counter. A cyanoacrylate fuming chamber and ninhydrin are available. The detective wants the magazine fumed immediately and the envelope treated with ninhydrin before anything else. You have one working fuming chamber, a DNA swabbing kit, and limited time before the medical examiner releases the body. The prosecutor has asked for a quick identification. You must decide a sequence that preserves the bloodstain pattern, DNA, and latent print evidence.
1. Propose a processing sequence for the metal magazine that preserves the bloodstain pattern, the blood DNA, and any touch DNA, and explain why each step is ordered that way.
Read the worked answer
Photograph the bloodstain pattern first with a scale and document its shape and location. Then swab the bloodstain with a sterile swab before any powder or cyanoacrylate is applied. Next swab the grip and trigger area for touch DNA with separate sterile swabs, air-dry them, and package separately. Only then should the magazine be fumed for latent prints or powdered. Reasoning: powder and cyanoacrylate can contaminate or obscure a bloodstain and may reduce DNA yield; the bloodstain pattern is fragile and must be recorded before handling. If the magazine is wet, air-dry it first. Change gloves between samples and use a negative control. If protocol requires fuming first, document the reason and sample DNA afterward with the expectation of lower yield.
2. After ninhydrin development on the paper envelope, the latent print shows 11 minutiae and a distorted delta; the candidate print is a partial from a known suspect. How do you assess suitability and what does an inconclusive conclusion require in documentation?
Read the worked answer
Assess clarity, distortion, quantity, and unique ridge detail. Eleven minutiae can be sufficient, but distortion at the delta and the partial nature of the print require caution. Use ACE-V: analysis of quality, clarity, and distortion; comparison with the candidate; evaluation of correspondence; and verification by another qualified examiner. If distortion prevents reliable correspondence, the conclusion is inconclusive. Documentation must state why: specific distorted areas, lack of corresponding ridge detail, inability to exclude, and the print's unsuitability for identification. Record all examiners, dates, methods, images, and limitations. Do not force a match based on minutiae count alone; the reasoning must show that the distortion was considered and why the comparison could not be carried to identification or exclusion.
3. A trainee asks why you would not fume the magazine before swabbing. Explain the reasoning and the conditions under which your answer might change.
Read the worked answer
Cyanoacrylate fuming deposits a polymer that can coat biological material; swabbing after may recover less DNA, and the bloodstain pattern may be obscured. The general sequence therefore favors DNA and pattern documentation first, then latent print processing. The answer might change if DNA is not probative-for example, if the blood is known to be the victim's-or if the magazine is dry and DNA has already been collected. It might also change if a validated laboratory sequence shows compatibility and the latent print is the priority. Even then, document the sequence and consider a DNA sample before fuming. The answer changes with the probative question, not with convenience or speed.