Wisconsin Lawyer
Vol. 75, No. 5, May
2002
Standards for Postconviction DNA Testing
Under Wis. Stat. section 974.07(7)(a), testing is required if:
1) The movant claims that he or she is innocent of the offense at
issue.
2) It is reasonably probable that the movant would not have been
prosecuted, convicted, found not guilty by reason of mental disease or
defect, or adjudicated delinquent ..., if exculpatory [DNA] testing
results had been available before the prosecution, conviction, finding
of not guilty, or adjudication for the offense.
3) The evidence to be tested meets the conditions under section
974.07(2)(a) to (c) [see below].
4) The chain of custody of the evidence to be tested establishes that
the evidence has not been tampered with, replaced, or altered in any
material respect or, if the chain of custody does not establish the
integrity of the evidence, the testing itself can establish the
integrity of the evidence.
Section 974.07(2) provides that a person may request DNA testing at
any time after conviction, adjudication, or commitment if all of the
following apply:
a) The evidence is relevant to the investigation or prosecution.
b) The evidence is in the actual or constructive possession of a
government agency.
c) The evidence has not previously been subjected to forensic [DNA]
testing or, if the evidence has previously been tested, it may now be
subjected to another test using a scientific technique that was not
available or was not used at the time of the previous testing and that
provides a reasonable likelihood of more accurate and probative
results.
Evolving DNA Profiling Technology
RFLP - Restriction Fragment Length Polymorphism
RFLP testing was the dominant form of DNA profiling from the
mid-1980s through much of the 1990s. This procedure produced excellent
results under the right circumstances. The testing was very
discriminating - that is, it could discern unique DNA profiles with
great precision, producing results identifying the odds of a random
match often in the range of one in several hundred million or even
billions. But the procedure had a flaw - it was not very sensitive. That
is, results could only be obtained from a fairly sizable sample of
biological material, such as a bloodstain about the size of a dime, with
DNA that was in good condition. In cases with minute samples, or old and
degraded samples, RFLP tests often were inconclusive.
PCR/STR - Polymerase Chain Reaction Using Short Tandem Repeats
RFLP has been replaced in recent years by PCR analysis using STRs.
PCR is a DNA replicating technique that allows testing on samples that
would have been insufficient for RFLP analysis. STRs are short segments
of DNA that differ from person to person, and can be used to create a
very discriminating profile. Following the lead of the FBI, 13 core
loci, or STR segments, have been established in this country as a
standard for DNA profiling and databanking. Using these STRs in
combination, DNA profiles are both highly sensitive - capable of
obtaining results from minute or degraded samples - and remarkably
discriminating - capable of producing odds of a random match often in
the range of one in many trillions or even quadrillions - far more than
the entire population on Earth.
Mitochondrial DNA Testing
A third type of testing has emerged in recent years that is being
used increasingly in criminal cases - mitochondrial DNA (mtDNA) testing.
Most DNA testing relies on DNA drawn from the nucleus of a cell. But
some biological material, such as hair shafts or bone, does not have a
nucleus and hence no nuclear DNA. Until recently, it was impossible to
do DNA testing on such material (testing on hairs could only be done if
the hair still had a root, which has nucleated cells). Now,
mitochondrial testing can get results from nonnucleated cells, by
analyzing the DNA in the mitochondria of such cells. The mitochondria,
however, do not contain the full complement of DNA; mitochondrial DNA
includes only the DNA inherited from the mother. Mitochondrial DNA
testing is essentially a single locus test and cannot discriminate
between family members in the line of descent; therefore it is not as
discriminating as nuclear DNA. Nonetheless, it can produce probative
results, and if the analysis produces an exclusion, that result is
conclusive.
Wisconsin
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