Metal deposition techniques for the detection and enhancement of latent fingerprints on semi-porous surfaces
- Publication Type:
- Thesis
- Issue Date:
- 2002
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Fingerprints can provide critical evidence in the investigation of crime. Most
fingerprints are latent, or invisible, and hence need detection and enhancement
before they can be used in the investigation of crime.
While techniques exist for fingerprint development on a range of surfaces, the
detection of prints on semi-porous substrates is particularly difficult. Vacuum metal
deposition (VMO) and multi-metal deposition (MMO) were investigated for their
ability to detect latent prints on such surfaces.
VMD is recognised as a very sensitive method of latent print visualisation but
inconsistent resu1ts are commonly encountered. This research shows that
reproducible VMD development is only obtainable when the amount of gold
deposited is carefully controlled. The type and quality of VMD development
obtained is influenced by a number of critical factors. These factors include the
amount of gold deposited, the polymer type of the surface being treated, the nature
of the latent print itself, and the presence of any other contaminants on the surface
(whether due to the history of the exhibit or treatment with other fingerprint
reagents).
MMD has not found routine application due to its complexity and mediocre results.
Recent research that sought to overcome these problems resulted in the development
of a new formulation known as MMDII. Several MMD formulations were trialled in
this study and MMDII proved to be the superior formulation, giving better overall
print detail. On non-porous surfaces, MMDII may offer further print development
than that achieved with cyanoacrylate fuming (CAF) and luminescent staining, but
VMD always gave superior results to MMD.
Polymer banknotes are a difficult semi-porous surface, causing particular problems
for fingerprint laboratories. A procedure utilising CAF followed by VMD and finally
luminescent staining enables successful print development on this substrate. Success
on new notes was achieved with prints up to 18 months old; unfortunately, the
possibility of successful print development decreases on used banknotes. VMD has
two important advantages for print visualisation on polymer notes: i) it is sensitive
enough to detect the small amounts of residue remaining; and, ii) the zinc layer
removes a significant amount of interference caused by the banknote design.
MMD and VMD were compared to standard techniques on other semi-porous
surfaces. MMD proved to be the technique of choice on these surfaces. The ability
of MMD to react with print residue within and on the surface is believed to be
important to its success.
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