Fingerprints, bite marks, hair samples, shell casings, etc. None of it is worth much. While this stuff can be used to prove that someone is not guilty, it's not of much use when it comes to determining guilt.
While actual junk science like bite marks has largely been discarded by prosecutors, the others remain, even as their reliability has been constantly questioned. The FBI loved hair analysis, right up to the point that it determined its witnesses had overstated test results 90% of the time in the two decades prior to 2000. Even fingerprints, which have long been considered unassailable because of their supposed uniqueness, aren't much better.
LINK: https://www.techdirt.com/articles/20160312/12192533885/scientists-looking-to-fix-many-problems-with-forensic-evidence.shtml