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.) |
