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Forensics Use of DNA: DNA in the Courtroom: Innocent or Guilty |
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Since the discovery of fingerprinting at
the turn of the century, science has assumed an increasingly important
and powerful role in the decision making process of our judicial
branch. We have seen that scientific testimony in the courtroom
can often be the determining factor for the outcome of civil and
criminal cases. The scientific analysis of fingerprints, blood,
semen, shreds of clothing, hair, weapons, tire tracks, and other
physical evidence at the crime scene can be more compelling to
a jury than the testimony of an eyewitness. With the dynamic effect
on the jury, DNA profiling has become a very controversial issue
that has to be addressed because it holds the power to change
the lives of many Americans by providing the evidence to prove
guilt or innocence. Without government standards and a uniform
procedure, are these methods valid, reliable, and admissible in
court?
DNA-identification testing in forensics
has been seen in the courts for close to ten years. The increasingly
widespread use of this technology by forensics in over a thousand
court cases has led to the intense review of all aspects of this
particular science, including the quality of the results and also
the scientific basis for derivation and interpretation of these
results. (Neufeld and Colman, p.52) Although DNA profiling techniques
and interpretation is common knowledge to molecular biologists,
many judges and juries, who are now continuously faced with it,
lack the biological information to understand this test. A gap
of knowledge has developed between biologists and law enforcement.
Not only are judges and juries unprepared, biologists do not comprehend
the legal consequences.
DNA profiling is actually a comparison of
DNA fragment lengths and patterns. DNA is isolated from the samples
to be compared and fragmented by a restriction enzyme. Then the
length of the resulting fragments determined by electrophoresis
and autoradiography are compared. These results are interpreted
in two steps, first a visual measured interpretation of the pattern
of DNA bands and if a match, the probability of finding a match
must be configured.(McElfresh, Vining-Forde, and Balazs, pp.149-150)
Previously, forensic scientists looked at
proteins to aid in some criminal cases but proteins have limitations
that DNA testing does not encounter. While blood-group analysis
and protein polymorphisms can be used to properly exclude someone,
it cannot identify an individual as a sole source of biological
material.(Moody, p.31) This type of analysis can only include
an individual in a specific group having traits in common. Also,
with traditional forensic methods, evidence may have to wait before
being examined, proteins can become degraded or denatured so their
antigenic properties are gone. (Moody, p. 31) For the use of forensics,
DNA is more suitable because DNA remains intact in the environments
where such evidence is found. The DNA molecule holds an impressive
stability to withstand time.
Without having a standard and uniform method
and procedure, there are many different techniques used throughout
courtrooms. As seen in the O.J.Simpson trial, restriction fragment
length polymorphism (RFLP) analysis is one procedure used and
the data it produces has been called a DNA fingerprint. This analysis
takes advantage of the concept that each person's DNA sequence
is unique. The first step in this analysis begins with the isolation
of DNA from the tissue sample. The DNA must be high-molecular-weight
DNA meaning, it must be undegraded by nucleases. The DNA is next
digested with a restriction endonuclease. The function of these
enzymes is to recognize and cut the DNA at specific regions. This
digestion process produces approximately one million DNA fragments
of differing lengths. Because the isolated DNA comes from a number
of cells, there are many copies of each DNA molecule. This endonuclease
digestion must be completed fully so that all molecules are cut
at all the possible sites. (Moody, p.32)
These restriction fragments are then separated
on the basis of their size in agarose gels. The process of gel
electrophoresis separates these fragments to allow them to be
analyzed. To identify specific fragments, scientists use a common
technique of molecular biology called the Southern blot. This
separates the strands of DNA double helix. The DNA fragments are
then transferred to a membrane filter while maintaining the pattern
of bands present in the gel. Radioactive probes are then added
which then bind to target fragments on the filter. There are two
different types of probes, single-locus and multilocus probe.
A single-locus probe is where the core sequence only occurs at
one DNA locus and multilocus probe is when there are many different
loci where the core sequence occurs.
The single-locus system is most commonly
used in forensic DNA identification. The autoradiograph resulting
from a single-locus probe will ordinarily show alleles of two
distinct sizes, one inherited from each parent. To determine whether
two samples of DNA come from a single source, you must examine
the bands identified by a particular probe on the autoradiograph
and determine whether they match. One must then look at the possibility
of a match within the population, thus to determine whether this
is unique. The probability of two individuals having the same
single locus DNA print by chance can be calculated by considering
the frequency of the different allelic forms of that locus in
the population. For example, if someone has an allele that is
present in only 1 out of 100 individuals, the frequency of that
allele would be .01 meaning a random match would occur 1 out of
100. (Moody, p.43) If alleles at three or four different sites
are evaluated, it becomes more unlikely that two individuals will
have the same alleles for all the sites. It is this notion that
gives DNA identification its persuasive power.
Another frequently used but less precise
technique that becomes an option for usage by forensic scientists
is known as the polymerase chain reaction (PCR). This is merely
a general test used to exclude a suspect from an investigation.
(New York Times, May 9, 1995) This was introduced in a court case
in 1986, Pennsylvania v. Pestinikas. Tissue samples from a corpse
were examined and the DNA in these samples was degraded, and there
was not a sufficient amount of high-molecular-weight DNA which
is needed by the RFLP analysis. The forensic scientists on the
case adopted the gene-amplification technique PCR. This technique
can make a million copies of specific DNA sequences. It does this
by using heat-stable DNA polymerase from the bacterium Thermus
aquaticus to direct repeated cycles of DNA synthesis from primers
that flank both ends of the gene. (Moody, p.35)
For the use of forensics, the PCR technique
is used to enlarge a multiallele locus, HLA-DQ alpha. The enlarged
DNA is then examined with allele specific probes in a dot-blot
hybridization, which is similar to the Southern blot. In dot-blot
hybridization, the DNA is not digested with restriction enzymes
nor separated by size in a gel. Instead, it is applied directly
to a filter membrane and then hybridized with a single-strand
DNA probe. The dot-blot hybridization only detects the presence
or absence of hybridization of the probe to the amplified DNA.
Therefore, if the test was done incorrectly, it would produce
a false result and you would not know that the error occurred.
This is different than the RFLP analysis because errors are readily
visible. Also, the gene frequencies are not low enough to identify
an individual as the sole possible source of a sample. However,
the PCR technique can be used to exclude individuals with certainty
some samples that cannot be analyzed by the RFLP analysis.
Not only are there many different techniques
used which causes problems in itself, difficulties arise that
further complicate DNA identification. One problem is the phenomenon
of band shifting. This occurs when DNA fragments migrate at different
speeds through separate lanes on a single gel. This problem has
been attributed to a number of factors including the preparation
of gels, the concentration of sample DNA, the amount of salt in
the DNA solution, and contamination. Band shifting can occur even
if the various lanes contain DNA from the same person. Because
allele sizes in forensic RFLP systems are closely spaced, it is
difficult to know if the relative positions of bands arise from
the size of the allele fragments or from band shifting. (Neufeld
and Colman, p.51)
In the courtroom, it may not be clear to
a lay audience that two bands that are not exactly aligned are
indeed a match. To a trained scientist, this phenomenon of band
shifting requires additional observation in the interpretation
of results but with adequate controls and a thorough analysis
of the test system an accurate interpretation of the results is
possible. Band shift was initially raised as a method of showing
that the results of a DNA case might be unreliable. The overall
question of band shifting in the use of DNA by forensics is if
two DNA patterns are not perfectly aligned, how can one be confident
that the patterns are indeed a match when the alternative is that
the suspect is released due to a nonmatch? Also, consideration
is needed to see if a band shift could produce a false positive.
The answer to that it is just as probable for a band shift to
shift away from a match than it is to shift to a match, there
is no way to predict what will happen. (McElfresh, Vining-Forde,
and Balazs, p.153)
Band shifting is one obstacle that must
be handled then by the court system and is an excellent example
of the problems that occur when the courts decide the reliability
of a method. Forensic DNA laboratories were working to develop
special probes that solve this problem.(Neufeld and Colman, p.51)
In a rape case tried in December of 1989 in Maine, State v. Mcleod,
the laboratory director who supervised the DNA tests for the prosecution
testified that a correction factor derived from a monomorphic
probe allowed him to declare a match even though the bands had
shifted. When evidence then came to light that a second monomorphic
probe indicated a smaller correction factor, which did not account
for the disparity between the bands, he acknowledged that the
monomorphic probes may yield inconsistent correction factors.
He argued that the first correction was appropriate, but the prosecutor
saw the foolishness of defending this argument without supporting
data and withdrew the DNA evidence.(Neufeld and Colman, p.51)
Without regulation, discrepancies appear forcing the evidence
not to be used.
Another major problem that arises in forensic
DNA typing is contamination. More often than not, crime-scene
specimens are contaminated or degraded. The presence of bacteria,
organic material, or degradation raises the risk of both false
positives and false negatives. An example of this would be when
contamination degrades DNA so that the larger fragments are destroyed.
Here, a probe that should yield two bands may yield only one.(Neufeld
and Colman, p.51)
What has to happen in order for DNA identification
to become legally accepted and a major component in the justice
system? To be admitted as evidence in a court case, a forensic
test should satisfy three criteria: the underlying scientific
theory must be considered valid by the scientific community; the
technique itself must be known to be reliable; and the technique
must be shown to have been properly applied in the particular
case. For a new type of evidence to be admissible, the judge must
be convinced of the technology's reliability and scientific acceptance
in a pretrial hearing called the Frye hearing. The guidelines
stem from the case Frye v. U.S. where the Court of Appeals for
the District of Columbia affirmed a lower court's decision to
exclude evidence derived from a precursor of the polygraph. The
court declared,
" Just when a scientific principle
or discovery crosses the line between the experimental and the
demonstrable stages it is difficult to define. Somewhere in this
twilight zone the evidential force of the principle must be recognized
and while courts will go a long way in admitting expert testimony
deduced from a well- recognized scientific principle or discovery,
the thing from which the deduction is made must be sufficiently
established to have gained general acceptance in the particular
field in which it belongs." (Lewis, p.6-7)
This leaves many legal and scientific professionals
feeling discontent with the Frye requirements. Scientists on the
stand must make complex molecular technology tangible and accessible.
The courts want to see what it is that makes the experts so sure
of their powerful conclusions. The courts are not willing to simply
believe expert witnesses just because they hold a specific position
or title. They want to be shown and given the opportunity to understand.
Some flaws of the Frye requirement is that it seeks demonstration rather than evaluation of the evidence or rationale behind such acceptance. In the past, the courts have looked to the qualifications of experts to validate the rather vague general acceptance requirement. The Frye procedure assumes that the judge and jury has the scientific background to evaluate the basis of general acceptance. The importance of the expert witness in evaluating the acceptability of new technology has been growing. It has been recommended that direct evaluation of scientific evidence replace the Frye procedure. The courts are demanding that they be shown why testimony of experts is valid rather than blindly accepting it.
The power of forensic DNA typing is its
ability not only to demonstrate that two samples have the same
pattern but also that that pattern is extremely rare. What is
missing in forensics is a set of adequate guidelines. In order
to use DNA evidence in court, there must be reliability and to
get this, there needs to be a national standard of the DNA identification
process for forensics. Today, there is a lot of data that backs
the validity of the DNA identification process, but at the same
time much variation exists which brings doubt. Just like any other
scientific fields, regulation and uniformity are the keys to building
acceptance and validity.
The FBI and other agencies have done thousands
of tests of DNA samples from many ethnic groups. It has confirmed
that the difference in DNA marker frequency are greater between
broad ethnic groups rather than in them. Now, the courts have
been asked to use the specific ethnic database to calculate the
possibility of a match when the race is known. If the race is
not known, the odds should be calculated using several different
population groups. This means that certain DNA markers are more
frequent in specific ethnic groups. Therefore, the odds should
be calculated specifying the ethnicity of the suspect. This will
allow prosecutors to determine the overall likelihood of a chance
match. This is the beginning of regulating this scientific field.
(Marshall, p.803-804)
There still remains concerns about the technology's
potential impact on civil rights of the accused suspect. For example,
what degree of probable cause must law enforcement officials demonstrate
before a judge can order a DNA blood test on an uncooperative
suspect? Also, can police officials use previously collected samples
for other purposes if they suspect an individual committed a crime.
These questions begin another debate about whether DNA should
be stored in a database for potential future use. Many worry about
the possible abuse that may develop and the possibility of false
accusation without probable cause.
As with any new technologies, the greatest
risk of reaching an incorrect conclusion stems from undetected
human error in the lab.(Marshall, p.803) Preliminary quality-control
surveys have revealed some serious errors in DNA labs, which probably
would have resulted in unjustified acquittals and convictions.(Weiss,
p.75) A researcher of the Whitehead Institute stated that he knows
they mess up and if you load the same specimen in both lanes,
you get an identity.(Weiss, p.75) Another problem that becomes
evident is that if a first test goes wrong, there usually is not
enough DNA to run the test again. This can be seen as frustrating
to many experts. The stakes get very high when molecular biology
comes out of the laboratory and into the courtroom.
DNA identification technology is becoming
a bigger and more important role in the justice system today.
Both the legal and scientific professionals are going to have
to work together to find common ground for which this evidence
can be viewed as valid, reliable, and completely certain. It begins
with educating the people and the court system of this new technology.
Standards need to be set and laboratories are going to have to
be structured similarly. The problems are going to occur when
different techniques are being displayed and when there is not
a consensus on a procedures. Within this field there must be standard
acceptance and uniformity. Without these, we will see doubt and
disbelief by judges and juries and many criminal cases may not
admit this evidence which could possibly solve the case. We have
the potential to prove the identity of the donor of biological
material at a crime scene. With a homicide occurring every 28
minutes and a rape every 6 minutes, this is quite an important
potential. (Lewis, p.9) We need guidelines and standards to make
this process reliable and valid for our courtrooms to use.
Aldhous, Peter. 1993. "Geneticists
Attack NRC Report As Scientifically Flawed." Science.
Vol.259, pp.755-756.
Lewin, Roger. 1989. "DNA Typing on
the Witness Stand." Science. Vol. 244, pp. 1033-1035.
Lewis, Ricki. 1989. "Genetics meets
Forensics." BioScience. Vol.39, No.1, pp.6-9.
Lewontin, R.C. and Daniel L. Hartl. 1991.
"Population Genetics in Forensic DNA Typing." Science.
Vol.254, pp.1745-1750.
Marshal, Eliot. 1996. "Academy's About-Face
on Forensic DNA." Science. Vol.272, pp.803-804.
Marx, Jean L. 1988. "DNA Fingerprinting
Takes the Witness Stand." Science. Vol. 240, pp. 1616-1618.
McElfresh, Kevin C., Debbie Vining-Forde,
and Ivan Balazs. 1993. "DNA-Based Identity Testing in Forensic
Science." BioScience. Vol.43, No. 3, pp.149-157.
Moody, Mark D. 1989. "DNA Analysis
in Forensic Science." BioScience. Vol.39, No.1, pp.31-35.
Neufeld, Peter J. and Neville Colman. 1990.
"When Science Takes the Witness Stand." Scientific
American. Vol. 262, No.5, pp.46-53.
"Simpson Judge and Jury To Learn All
About DNA," The New York Times, May 9, 1995. p.A22.
Weiss, Rick. 1989. "DNA Takes the Stand."
Science News. Vol.136, pp.74-76. | |||
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