April 1996

            Hidden Evidence: Latent Prints on Human Skin

                       By Ivan Ross Futrell

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Mr. Futrell is a supervisory fingerprint specialist in the
Latent Fingerprint Section of the FBI Laboratory in Washington, D.C.
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(Recent research proves that identifiable prints can be
 obtained from the skin of homicide victims under real
 field conditions, not just in the laboratory.)


Whether to stop them from fleeing, immobilize them, or 
dispose of them, murderers often grab their victims. What 
homicide detective has not wished for the ability to 
develop identifiable fingerprints of a suspect from the 
skin of a dead body? Crucial fingerprint evidence linking 
the perpetrator to the victim must be right there, but, 
until recently, attempts to retrieve those prints rarely 
met with success.

Skin possesses a number of unique qualities that
distinguish it from other specimens examined for latent 
prints. Skin tissue grows and constantly renews itself, 
shedding old cells that might contain the imprint of an 
assailant's grip. Its pliability allows movement and, 
hence, possible distortion of fingerprints. As the skin 
regulates the body's temperature and excretes waste matter
through perspiration, latent prints can be washed away.

In addition to these natural changes, the skin of homicide
victims often is subjected to many harsh conditions, such
as mutilation, bodily fluids, the weather, and 
decomposition after death. Further, during crime scene 
processing, many people might handle a body while removing
it from the scene, which also can destroy existing
fingerprints or possibly add new ones to the 
corpse's skin.

In spite of these hurdles, research conducted by the FBI
Laboratory's Latent Fingerprint Section--in 
conjunction with police and medical authorities in 
Knoxville, Tennessee--proves that latent fingerprints can
be lifted from skin if only investigators are willing to
try. This article outlines the history and research that
led to development of a workable method for developing
identifiable latent prints on human skin.

HISTORY

The FBI has been involved in research on methods to 
develop identifiable latent prints on human skin for many
years. In the early 1970s, FBI scientists reexamined
existing methods using cadavers at a major university and
the Virginia State Medical Examiner's Office in Richmond,
Virginia. Most of these cadavers had been embalmed.

To create prints, these researchers applied a coating of
baby oil and petroleum jelly to their hands and then 
touched areas of skin on the cadavers. At timed intervals,
they then attempted to develop these latent prints, using
primarily the iodine/silver transfer method. This method 
has five steps: heating iodine in an iodine fuming gun,
directing the fumes onto the skin, laying a thin sheet of
silver on the skin, removing the silver plate and, 
finally, exposing the plate to a strong light, which 
causes the prints to become visible.

The researchers developed identifiable prints in this
fashion within a time frame that ranged from several hours
up to several days after the prints were applied. It
should be noted, however, that the researchers achieved
these results under ideal laboratory conditions. It was
not surprising that they developed latent prints composed
of artificially introduced oily substances on embalmed
cadavers. Yet, those early efforts provided important
background data for subsequent research conducted in
Tennessee.

In 1991, a police specialist from the Knoxville,
Tennessee, Police Department contacted the FBI Latent
Fingerprint Section to inquire about the FBI's experience
and previous research on developing latent prints on
skin. His own examination of numerous homicide victims
had not produced prints with identifiable ridge detail,
even though some cadavers exhibited observable outlines 
of fingers and palms. Out of these discussions arose a
joint research project involving the Knoxville Police
Department, the University of Tennessee Hospital, the
Department of Anthropology at the University of
Tennessee, and the FBI.

To develop a consistent and reliable technique for
developing latent prints on skin, the researchers
established a protocol significantly different from
previous efforts. They decided to use only unembalmed
cadavers and to place latent prints composed of only
natural perspiration and sebaceous (oily) material. They
felt that such conditions more accurately replicated 
field conditions faced by police investigators.

RESEARCH

The researchers first examined the body of a 62-year-old
white female who had been dead for 9 days. Areas of skin
were sectioned into numbered squares drawn on the body.
One researcher placed latent prints on the skin by wiping
his hand across his brow or through his hair and then
touching the cadaver. The researchers then tried to
develop the latent prints at timed intervals by employing
several methods, including the use of lasers, alternate
light sources, iodine/silver transfer, cyanoacrylate
fuming (commonly referred to as "glue fuming"), regular
and fluorescent powders, specially formulated powders,
regular and fluorescent magnetic powders, liquid iodine,
RAM, ardrox, and thenoyl europium chelate.1

Most of these methods developed the latent prints up to
approximately 1 hour after the prints had been deposited.
For additional documentation, during the next several
days, researchers tested the techniques on other
cadavers, but most methods failed to provide consistent
results.

The one technique that developed identifiable latent
prints most often was glue fuming in conjunction with
regular magnetic fingerprint powder. Similar to
iodine/silver transfer, this method involves heating glue
and directing the fumes onto the skin, then applying
fingerprint powder to reveal the latent prints.

To test this technique further, researchers glue fumed
several areas of skin containing sebaceous latent prints
2 hours after depositing the prints. Sixteen hours later,
they applied various fingerprint powders to those
areas. Using a fluorescent powder specially formulated
for this testing, they developed a latent print of value
for identification purposes. Initially, the researchers
believed that the special fluorescent powder provided the
key to obtaining usable prints, but additional tests
proved that the type of powder did not matter as much as
the amount of time allowed for glue fuming.

Glue Fuming Device

As they continued their research, the scientists realized
that they needed an improved method for spreading glue
fumes over the skin. The earlier method used--forming an
airtight plastic tent over a small area of skin or over
an entire body--did not always work. It was impossible to
distribute glue fumes evenly over the skin and extremely
difficult to confine all of the fumes to the tent. In
addition, when they removed the plastic tent at the end
of the fuming process, the fumes often forced the 
researchers out of the work area. To alleviate these
problems, one of the researchers, the police specialist
from the Knoxville Department, developed a portable glue
fuming chamber.

The glue fuming chamber contains a built-in heat source
and a small electric fan. Glue is poured into a small
disposable preheated aluminum pan and placed in the
chamber. After approximately 5 minutes, the fan is turned
on and the glue fumes flow out through a plastic hose
attached to the top of the chamber. When set at maximum,
the amount of fumes forced through the hose approximates
the exhaust from an automobile on a cold day. This device
enables the user to control the amount and time of the
glue fuming much more easily than the tent method.

Using the new device, the scientists tested squares of
skin to determine the optimal fuming time. They tried
fuming in increments from 5 seconds up to 2 minutes. They
obtained identifiable latent prints most often when
glue fumes had been applied to the skin for 10 to 15
seconds.

Powders

In the early testing, it seemed that particular types and
brands of fingerprint powders provided the best results.
As the research progressed, however, it became apparent
that this was not the case. More than 30 brands and
several types of powders and applicators were tested. In
the end, researchers determined that powder selection
is less critical than ensuring that the glue fuming
process is performed correctly.

Both fluorescent powders and regular magnetic powders
produce identifiable prints. With non-magnetic 
fluorescent powders, the best results are obtained by 
applying the powder with a feather duster rather than a 
conventional brush, which generally holds more powder. Too
much fluorescent powder tends to overwhelm the latent
print and the background. While fluorescent powders work,
they do have some drawbacks. They generally cost
more than regular magnetic powders, are more difficult to
see, and require special light sources, filters, and
additional photographic knowledge.

In comparison, regular black magnetic powders produce
useful prints and cost much less. They also do not
require special photographic skills. Indeed, technology
does not need to be complex or costly in order to be
effective.

Field Conditions

Developing latent prints under ideal laboratory conditions
proved that prints could be obtained from human skin, but
the researchers wanted to make sure that practitioners in
the field could obtain similar results. In real life,
homicide victims might not be found immediately, bodies
might be exposed to the elements or other harsh
conditions, or they might be taken to the morgue and
refrigerated before they can be examined for prints.

To ensure that the process would work, the researchers
simulated field conditions by testing cadavers that had
been exposed to the elements for several days, as well as
refrigerated corpses. They replicated potential time
delays that could occur in the field by waiting for 
approximately 12 hours between the glue fuming (which 
could be done at the crime scene) and the application of 
fingerprint powders (perhaps conducted later at the
morgue). The results showed that by following proper 
procedures, investigators could develop identifiable 
latent prints even under harsh conditions.


RECOMMENDATIONS

This research indicates that homicide victims should be
examined for latent prints whenever investigators believe
that the perpetrator touched the victim. If possible, 
bodies should be examined at the crime scene immediately
after the coroner or medical examiner has completed an 
initial examination and granted permission. At a minimum,
the body should be glue fumed at the scene to preserve
the prints and help prevent contamination or obliteration 
of prints when the body is moved.

Ideally, bodies should not be refrigerated prior to
examination for latent prints. The condensation that
builds up on refrigerated bodies can have adverse effects
by washing away the prints, reacting with the glue to
distort the prints, or causing the powder to cake, thus 
losing the prints. Bodies that have been refrigerated
should not be processed until the moisture evaporates,
roughly several minutes, depending on ambient 
temperature. A control area of skin least likely to have
prints can be tested to ensure that the moisture has
dissipated.

Skin that is warm or near normal body temperature should
be glue fumed for only 5 to 10 seconds. Colder skin
should be glue fumed for a maximum of 15 seconds. Regular
magnetic powders can then be applied. Any
identifiable latent prints should be photographed first
and then lifted using transparent lifting tape.

CONCLUSION

For many years, investigators and forensic scientists have
tried to retrieve latent prints from dead bodies, 
but often the key evidence has been just out of reach.
Frustrated, investigators often gave up after several
failed attempts. This research proves that with practice,
it can be done by those who are willing to try.
As it becomes routine for law enforcement to obtain
latent prints from skin, murderers who reach out to harm 
their victims will just be putting themselves within easy
reach of the long arm of the law.

_________________
Endnote

These are commonly used methods for developing latent
fingerprints on a variety of surfaces. For more
information, see Chemical Formulas and Processing Guide
for Developing Latent Prints (Washington, DC: Latent
Fingerprint Section, Laboratory Division, FBI, 1994).

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