Examination of Firearms Review: 2007 to 2010 - Interpol

investigated (216-218), as well as the effect of pressure and sweat on the
quality of ninhydrin-processed fingermarks (219). An alternative to the use
of a temperature- and humidity-controlled development cupboard has also
been proposed (220). Concerning DFO, Schwarz and Beisel proposed a
new formulation, said to be more robust against the formation of two
phases (221). The studies on 1,2-indanedione were mainly focused on the
optimization of the formulations and of the development procedures (222-
224). Finally, lawsone (225) and isatin (226) were proposed as new
promising amino acid reagents, while pDMAC was proved to actually react
with amino acids, and not with urea as it was thought for long (227).
Ninhydrin and analogues
A computational study, initiated by Petraco et al. (see Interpol report 2004-2007) on
the reaction mechanisms between ninhydrin (and analogues) and amino acids, has
been pursued (216). According to their conclusions, some analogues could constitute
promising substitutes for ninhydrin and should be synthesized for experimental tests.
Following their research on a one-stage “ninhydrin / metal salt” premix formulation
behaving like a dual reagent (i.e., leading to both coloured and luminescent
fingermarks), Almog et al. showed that the use of commercially available ninhydrin
analogues led to better results (217). By mixing 5-methoxyninhydrin (MN) or 5methylthioninhydrin
(MTN) with zinc or cadmium salts, coloured fingermarks could be
obtained (MN: orange with zinc, and pink with cadmium; MTN: pink with zinc, and red
with cadmium) and observed in luminescence at room temperature, without the use
of liquid nitrogen. The “MTN ⁄ ZnCl2” gave the best results, with fluorescence intensity
comparable to the one of 1,8-diazafluoren-9-one (DFO), but with a much stronger
visible colour. If classified according to the colour, the different reagents were ranked
as follows: MTN/ZnCl2 ≅ MN/ZnCl2 > Ninhydrin/ZnCl2 > DFO. If the classification is
made according to the fluorescence intensity at room temperature: MTN/ZnCl2 =
DFO ≥ MN/ZnCl2 >> Ninhydrin/ZnCl2.
Jasuja et al. investigated the effect of various parameters that occur during the
deposition of a fingermark on the efficiency of the subsequent ninhydrin process
(219). For this study, thirty individuals (among which five were considered as good
sweat donors, and five as bad sweat donors) aged from 20 to 25 years left latent
eccrine marks on white paper following different conditions: conventional situation
(no specific pressure, no induced sweat), with pressure (i.e., 50 g, 100 g, 150 g, and
200 g), and with induced sweat production before deposition using a polyethylene
bag around the hand (i.e., for 30 to 180 seconds). Less than 24 hours later, all the
fingermarks were processed using ninhydrin. Linear relations were established
between the quality of the developed marks and the pressure intensity, under the
studied conditions. As the induced sweating time increases, the quality of the marks
increased as well for all types of donors (mixed, good and bad donors). An induced
sweating time of 120 seconds produced the same quality of development of the
fingermarks, irrespective of the donor quality. In case of good sweat donors,
smudging of the fingermarks could occur when the pressure applied and induced
sweating time exceeded 200 g and 180 seconds, respectively. On the contrary, in the
case of the bad donors, greater pressure and induced sweating times definitely
resulted in marks of better quality.
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