The Use
of the Rubber Stamp Analogy in Fingerprint
Testimony
By Jim McNutt,
Sedgwick County Sheriff's Department,
Wichita Kansas.
One very important element of fingerprint
testimony is communicating effectively with
the jury. Fingerprint testimony needs to be
explained in clear, simple terms so that all
members of the jury will understand it. If
jurors cannot understand what the expert is
saying they may choose not to listen, or
give the testimony little weight during
deliberations. One method of explaining
things in easily understood terms is through
the use of an analogy. One of the best
analogies for fingerprints is a rubber
stamp. A rubber stamp, specifically an
address stamp, has many things in common
with a fingerprint. It is something that
most jurors are going to be familiar with
and they should easily be able to compare
the two and gain a better understanding of
fingerprints. The following table compares
fingerprints and a rubber stamp in several
different ways that could apply during
testimony.
|
Fingerprint
|
Rubber Stamp
|
| Has raised portions
of skin. |
Has raised letters |
| Ridges are
permanent. Ridges do not change, but
may be damaged by- scars or burns. |
Letters are
permanent. Letters do not change
unless damaged, such as cutting a
letter with
a knife. |
| Fingerprints are
unique. No two people have the same
fingerprints. |
An address stamp is
unique. No one else has
the same address. |
| Leaves a residue in
sweat, grease, blood, ect. This
residue is transferred to another
surface in the same arrangement as
the ridges on the finger. |
Leaves a residue in
ink. The residue is transfer red to
another surface in the same
arrangement as the letters on the
stamp. |
| There must be sweat,
or some other substance on the
fingers to transfer. |
There must be ink on
the letters to transfer. |
| Surface must be dean
and smooth, receptive to a latent
print. On a dirty surface the
residue will not transfer through
the dire. A textured surface will
break up the ridge detail making the
print illegible. |
The surface must be
clean and smooth and
receptive to the ink. Ink will not
transfer
through dirt. A rough surface breaks
up the lettering and won't be able
to read it. |
| Need a clean touch
and release of the finger on the
surface. Can leave an impression
that is blurred, smeared, faint,
incomplete, or overlaid. |
Can leave impression
that's blurred, smeared
faint, incomplete, or overlaid. If
the stamp were pressed down and drug
across the paper it would be
unreadable. |
| Even a partial print
is identifiable. |
Even part of an
address is identifiable. If you
were to see your last name, street,
and city, you would still know it
was yours. |
| If left on
non-porous surface, it may be rubbed
off. The residue could soak into a
porous surface. |
Ink can be rubbed
off a non-porous surface,
like glass. It could soak into a
porous surface, like a paper towel. |
By just looking at
the fingers, the fingerprints are
reversed, from what they look like
when
put on a surface. |
When looking at a
rubber stamp, the letters look
reversed. They are oriented
correctly when stamped on a piece of
paper. |
Individual ridges
have unique shapes.
(Level 3 detail) |
Individual letters
can have unique shapes. Font type
and point size. |
It will seldom, be necessary to use all
of these comparisons during testimony. What
I have used effectively in the past is to
touch on two or three of them when
explaining what a latent fingerprint is. I
usually talk about the raised skin and
raised letters on the stamp and that they
are both covered with a residue and
transferred to another surface. If the
prosecutor or defense asks a question that
another one of these comparisons may apply
to I will ask the jury to recall the rubber
stamp analogy and use that to answer the
question. The finger print examiner often
takes the role of teacher when testifying to
a jury. The jury needs to understand and
remember what a latent fingerprint is. By
using the rubber stamp analogy a fingerprint
examiner can help can help the jury gain
this understanding and give the fingerprint
evidence full consideration during their
deliberations.
References
Ashbaugh, D.r., "Ridgeology" Journal of
Forensic Identification, 41 (1), 1991, pp.
16-64.
Hazen, Robert J., and Charles E. Phillips,
"The Expert Fingerprint Witness,"
U.S.D.O.J., F.B.I.,
U.S. Government Printing Office, Washington,
D.C., 1981.
Wertheim, Pat A., "Qualifying as an Expert
Witness: designing a Set of Questions to
Assist
In Court Testimony," Journal of Forensic
Identification, 40 (2), 1990, pp. 60-67.
(Thanks Jim for submitting this article. I
would also like to mention that Jim recently
passed the IAI Latent
Print Certification testing. Congratulations
on completing such a difficult task.)
|
