Law Enforcement
Resources
For details about sending us a case, please
look under Submit
a Case.
We are often asked about the "best"
samples for DNA testing. Generally, for hair
submission:
- We suggest that you select candidate questioned
(evidentiary) hairs based on their probative
value. For example, a hair taken from the
floor of a public rest room near a victim's
body may be
less informative than a hair found on the
victim. Samples can be prioritized to save
financial resources. We can perform your testing
accordingly.
- We suggest that a qualified hair examiner
evaluate evidentiary hairs with respect to
each other. Microscopic hair comparison may
be less valuable as a tool to compare questioned
hairs to the
exemplar hairs of known individuals than as
a tool to compare questioned hairs to each
other. Then, depending on their probative
value, candidate hairs can be selected from
groupings of
similar hairs for testing.
- All other variables being equal, such as
equally probative and similar-appearing hairs,
we prefer to take a portion of a longer hair,
rather than consume an entire hair. Preservation
of evidence
is important whenever possible. In general,
the size of hair sample taken for testing
will be about 2 cm, if available, but this
varies according to numerous considerations.
We do not advocate against testing small hairs
simply because of their size and because they
will be consumed. We have successfully analyzed
hairs as small as 2 mm and the challenges
of testing small hairs are similar to the
challenges of testing any small or old sample.
In the event that a hair is consumed, a review
of the laboratory case folder by opposing
counsel (discovery) is more desirable than
not testing potentially informative evidence.
- Reference samples provided for comparison
to hair samples do not need to be hairs.
In a rare case hairs might be requested for
a reason. However, in most cases, a buccal
swab, saliva, or blood reference known is
acceptable. We will discuss with you any situation
in which a family reference sample might be
needed when a direct reference sample from
an individual is unavailable.
- Hair samples may be submitted on slides,
post-it notes, on tape lifts, in small tubes,
paperfolds, coin envelopes, or zipper seal
plastic bags. If hairs are mounted on slides,
we prefer to remove the hairs from the slides
ourselves, as reduced handling reduces the
possibility of contamination. However, the
exception to this rule is if hairs and trace
(fibers) are all mounted together on slides,
we prefer that either the trace be removed
or that the hairs be removed and repackaged.
- In any case, we recommend that any necessary
microscopy or photodocumentation of hair or
other evidence be completed prior to sample
submission.
Here are some general thoughts on skeletal
sample submission:
- Unless very old, skeletal remains are usually
very successful samples, with rare exceptions.
In order of preference, we prefer these samples
due to their likelihood of containing good
quality mtDNA: tooth, long bone (femur, radius,
humerus, ulna, tibia, fibula), rib. However,
any skeletal material can
be tested, even the smallest fetal remains.
- For teeth, in order we prefer: unreconstructed
molar/premolar, unreconstructed canine, unreconstructed
incisor, teeth with dental work. We remove
the dental work and return it.
- About 0.4 g of powdered tooth or bone is
used in an analysis. Remaining bone powder
is returned along with uncut skeletal or tooth
samples.
- Again, we recommend that any necessary microscopy
or photodocumentation of skeletal evidence
be completed prior to sample submission.
Other samples:
- We have tested many sample types, including
fingernails, organ tissue (slides, paraffin),
cigarette butts, touched or licked objects,
fabric cuttings, surface swabs, and clothing
swatches, among
others. Please call us to discuss the limitations
of mitochondrial DNA analysis on some of these
sample types.
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