Two CT men did 30 years for murder on the basis of a forensics expert’s testimony that a towel of theirs had blood from the (horrifically bloody) crime scene. The towel hadn’t been tested, and it wasn’t even blood. Brutal rebuke from state Supreme Court.
Not only can blood spatter analysis be wrong; sometimes the evidence isn't even blood. Two men were convicted of murder in 1989, in part on Dr. Lee's testimony about a bloody towel. Turns out it wasn't blood after all.