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Issues in Criminal Justice Technology & Security
How it works:
Most common form uses polymerase
chain reaction to make millions of copies of very small amounts
of DNA. Lab can use them to generate DNA profiles, which compare
scans of 13 DNA regions varying from person to person (only identical
twins are likely to have the same combination), which are then
compared to individual's DNA profile. Then lab generates a statistic
to show how frequently you'd expect to find this DNA profile in
general population. DNA analysis is a major step forward: Previously,
"it was possible to exclude a suspect, but evidence for inclusion
was weaker than it is now because the probability of a coincidental
match was larger."
3 Possible results:
- inclusion: when a victim's or
suspect's DNA profile is consistent with that gathered from crime
scene, the individual is "included" as possible source.
"However, the strength of inclusion depends upon the number
of loci (locations on the DNA strand) examined and how common
or rare the resulting DNA profile is in the general population."
- Exclusion: if the DNA profile
from a victim or suspect is inconsistent with the crime-scene
DNA profile. "However, exclusion does not imply innocence.
In a rape case, for example, a perpetrator wearing a condom could
be excluded as a suspect because no semen was found at the crime
scene, but evidence found elsewhere at the crime scene may include
that same person as a suspect."
- Inconclusive: could neither
include or exclude individual as the source. "Inconclusive
results can occur for many reasons: for example, the quality
or quantity of DNA may be insufficient to produce interpretable
results, or the evidentiary sample may containa mixture of DNA
from several individuals (e.g., a sample taken from a victim
of a gang rape)."
Benefits of DNA testing:
As
we learned in the historical section of the course, it is now increasingly accepted in courtroom.
"This does not necessarily mean that DNA evidence alone can
determine a verdict. DNA evidence is used often to corroborate
eyewitness testimony or other evidence. The increased use of DNA
evidence also has made it important for victim service providers
to become familiar with DNA terminology and DNA evidence collection,
examination, and preservation procedures"
--The
Evolution and Development of Police Technology
Rapidly advancing science and
application:
- National Academy of Science
study in 1992: DNA
Technology in Forensic Science, said it "strongly
supported the validity of DNA testing."
- can determine sample's DNA profile
in 1-2 days, vs. 6-8 weeks when first introduced in 1980s.
- Because of the Human
Genome Project, there's now prospect of being able to make
absolute identification of an individual.
- FBI now maintains a nationwide DNA database:
CODIS.
- A 2000 report, "The
Future of Forensic DNA Testing," predicted that, "Within
10 years we expect portable, miniaturized instrumentation that
will provide analysis at the crime scene with computer-linked
remote analysis. This should permit rapid
identification and, in particular, quick elimination of innocent
suspects."
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