Finally, many people don't realize that DNA testing can be done on old and even partially degraded material, although the value of the results may be compromised if the samples were contaminated as a result of having been improperly collected or stored. It is almost uniformally accepted by state courts and is accepted in all federal courts. Testimony about the DNA testing can be confusing. There is basic agreement that the underlying science of the DNA testing is not open to serious challenge. Opposition, such as exists, may be directed to the specifics of the particular tests done or, reflect a reluctance on the part of the defendant to accept an inclusion or a prosecutor to accept an exclusion, especially where it might require reversal and dismissal of a case which had been previously tried to a conviction.
Hair poses particular challenges.
The strands themselves will not generate a profile through application of standard DNA testing, which requires the presence of the hair follicle. New advances in mitochondrial DNA testing have produced accepted tests results in recent cases. This testing is prohibitively expensive and is, at this time, only being done by the FBI laboratory. Each can offer the same information with the same degree of precision. Clearly, taking a saliva sample from a suspect is the least physically intrusive.