A successful lift

Not every crime scene is straightforward. Sometimes a crime scene officer is required to lift a fingerprint from surfaces that can’t be taken back to the laboratory, so ensuring the best technique is applied is key to recovering evidence and solving the crime.

Small particle reagent (SPR) is a fingerprint development technique used for the enhancement of latent marks on wet non-porous surfaces, but can also be used on porous and adhesive surfaces.
SPR is a reagent containing an insoluble powder; conventionally molybdenum disulfide, in an aqueous suspension also containing the surfactant tergitol. It physically develops latent fingerprints when it is sprayed onto the suspected area, allowing the powder particles to adhere to the water insoluble substances of the deposits such as the oily constituents in the print residue.
The technique is frequently applied at crime scenes when an item cannot be taken back to the laboratory immediately for further examinations. A vehicle wet with rain or even recovered from a lake or pool, for example, is a common item that would require the SPR technique to be used.
Because of this, it is important that SPR recovery of fingerprints is successful. With that in mind, Zeeny Shah, a forensic student from the University of Derby’s Department of Biological and Forensic Sciences, began a project to determine ‘the optimal method for the development and enhancement of small particle reagent developed latent prints’.

Method
In her study, Ms Shah tested four different methodologies for optimal recovery of SPR print on wet non-porous surfaces for their ability to develop minutiae – comparable features of a fingerprint.
“Sixteen minutiae were identified in a standard ink print (figure one) and the presence of these minutiae was looked for in developed SPR prints,” said Ms Shah.
Two of the most successful SPR methodologies were then tested with enhancement techniques.
Firstly, SPR and distilled water was alternated onto the latent print until it is visible. “The method involved laying down fingerprints from a donor then wetting the item in question before using SPR to develop any latent marks – carried out by dripping or spraying – and then washing off the excess SPR using distilled water so that ridge detail can be observed,” said Ms Shah.
Secondly, SPR was sprayed on a latent print, left for five minutes before being rinsed with distilled water.
The optimum method was then enhanced with magnetic powder, GREENescent, which fluoresces brilliantly when exposed to forensic light sources, and a novel compound known as pyrocatechol violet.

Results
From preliminary findings, Ms Shah said: “Of the methods tested, print-wet SPR+distilled water was discovered to develop the most minutiae from a model print (20 per cent).”
Several methodologies for using SPR were tested (figure one) and two of these methods developed a higher percentage of the minutiae from the control print than the others. These two different methods were further enhanced by three chemicals (figures two and figures three).
Enhancement using magnetic powder provided the best results with an 81 per cent increase in visible minutiae.
All enhancement techniques showed some improvement in the number of minutiae visualised.
“The results show that enhancement of SPR developed marks can enhance the amount of minutiae visualised,” said Ms Shah. “In one case no minutiae were visible until enhancement with magnetic powder was carried out.
“Though successful, two out of the three dyes tested were suspected carcinogens; making them unsafe and undesirable for use at a crime scene. This study has shown that using magnetic powder or other non-harmful enhancement techniques can give excellent results and are useful in-situ to enhance SPR-developed fingerprints.”
Other potential uses include:
•Processing non-porous items covered in water or snow.
•Developing latent prints on non-porous items that have been lightly washe