With the continuing development of forensic sciences, the Courts have assumed the role of gatekeepers when it comes to admissibility. You can get into the details as deeply as you like on sites like
The National Library of Medicine, which has an article describing the different analytical frameworks courts apply, and cases decided under those frameworks.
People who live in the American West will not be surprised to learn that Idaho has decided to go its own way on this subject, adopting a standard that seems much broader than other states and the US Court system:
"
Idaho Rules of Evidence Rule 702. Testimony by Expert Witnesses.
A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if the expert's scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue."
MOO, BK will challenge expert analysis of DNA under this test, both as support for search warrants and as evidence for the inference that he was at the murder scene with a weapon. I note with interest that the lead investigator specifically asked the court to ignore the DNA evidence in its analysis of probable cause to arrest. I expect (MOO) this is a standard precautionary strategy, i.e. not wanting to rely too heavily on DNA in case there were errors in handling or processing that reduce its reliability and call the arrest and incident searches into question. But it could have other significance for speculative minds.
Most of the reported cases seem to support the admissibility of DNA expert testimony even when its reliability or relevance to a particular fact in issue may be questioned. After decades of reliance on DNA science, judges seem to prefer to let juries sort these issues. Again, MOO - and I am always prepared to be surprised...