Latent Print Development - National Criminal Justice Reference ...

Although squalene composition changes with donor age,
the range is not very significant. The concentration of squalene
begins at 9.9% for newborns and reaches a low of
6.2% in children of ages 2–4 years. The concentration then
slowly begins to rise in children 4–8 years in age (7.7%) and
peaks at a value of 12% in postadolescents.
7.2.5 Latent Print Residue
A latent print is a mixture of some or all of the secretions
from the three types of glands. The amount of material
contained in a latent print deposit is rather small, typically
less than 10 μg, and has an average thickness of about
0.1 μm (Scruton et al., 1975, pp 714–723). The latent print
secretion is a complex emulsification of these numerous
and varying compounds. When deposited on a surface,
nearly 99% of the print is composed of water. As this water
begins to evaporate rapidly from the deposit, the print
begins to dry out. This process begins to alter certain reagents’
ability to visualize the print. Fingerprint powder, for
example, will not work as well on a dried-out latent print,
but other processes, like ninhydrin and physical developer,
have developed prints several years old (McDiarmid, 1992,
pp 21–24).
Latent print residue is generally divided into two basic
categories, water-soluble and water-insoluble. The watersoluble
portion of the print deposit is typically composed
of eccrine secretions like salts (e.g., NaCl) and amino acids
(e.g., serine, glycine). Chemicals like ninhydrin (which
reacts with amino acids) and silver nitrate (which reacts
with sodium chloride) are effective reagents for visualizing
this water-soluble portion of the residue. However, an
eccrine-rich latent print that is exposed to water most likely
will not be recovered with these methods. This is why,
before the introduction of physical developer in the 1970s,
there was no reliable method for recovering prints from
water-soaked documents.
The water-insoluble portion can really be divided into two
subcategories. One fraction of this residue is composed
of large, water-insoluble molecules (e.g., proteins) and the
other fraction is composed mainly of nonpolar lipids (e.g.,
fatty acids). Reagents like physical developer are thought
to react with compounds similar to the first fraction, and
reagents like Oil Red O or Nile Red react with lipids from
the second fraction.
Latent Print Development C H A P T E R 7
7.2.6 Aging of Latent Print Residue
A number of laboratories have looked into studying the
changes in the composition of latent print residue and have
determined that the composition of latent print residue can
change dramatically over time. The foundation work in this
area was conducted during the 1960s and 1970s by the
U.K. Home Office Scientific Research and Development
Branch and Central Research Establishment (Bowman et
al., 2003, pp 2–3). Additional studies have been conducted
by some of the Home Office Forensic Science Service
laboratories and several Department of Energy National
Laboratories.
7.2.7 Home Office Scientific Development
Branch (U.K.)
The U.K. Home Office sponsored a number of research
efforts, which were carried out by two groups: the Scientific
Research and Development Branch (also known
as the Police Scientific Development Branch [PSDB] and
currently known as the Scientific Development Branch) and
the Central Research Establishment. A number of studies
conducted in the mid- to late 1960s looked at determining
the amount of certain inorganic compounds (chlorides)
(Cuthbertson, 1969) as well as lipids (Wilson and Darke,
1978) in latent print residue. These studies did not address
the changes in composition with time. However, one study
monitored the change in chlorides, amino acids (as leucine),
and urea concentration in a deposit over the course
of 236 days (Knowles, 1978, pp 713–721). After 236 days,
the chloride concentration had changed from 0.223 μg/cm2 to 0.217 μg/cm2 . The amino acid content had changed from
0.083 μg/cm2 to 0.046 μg/cm2 , and the urea content from
0.083 μg/cm2 to 0.028 μg/cm2 .
The PSDB recently sponsored some work in this area
(Fitzgerald, 2003). A project was started in February 2002
between the University of Lincoln and PSDB to look into
the gas chromatography–mass spectroscopy (GC–MS)
analysis of the composition of latent print residue and how
it changes over time.
7.2.8 Home Office Forensic Science Service
(U.K.)
The U.K. Home Office Forensic Science Service (FSS) has
also been active in the area of latent print chemistry. The
FSS conducted an early preliminary study in conjunction
7–9