I do agree that police need to be careful with DNA evidence and not use it as proof of guilt where it implies no such thing, but that does not seem to be the case here.
You can't even say that for sure here. I've played with a cigarette lighter before and the one thing I recall is I quickly rubbed my thumb raw. Needless to say, a lot of DNA came off in the process. If the girl did use the lighter after him, that could easily explain his DNA embedded in her fingers, but the fact it would have ended up on her fingers could explain it ending up a lot of other places too. Ever rub your eyes, blow your nose, scratch your crotch or wipe your
Add to that, the guy is 44 years old and has never committed a crime nor even been a suspect until now. Granted, he was 31 when the crime occurred but he was quite old even for the type of behavior required to commit such a brutal crime to come to the surface. The fact nothing is known of him since would make it even more unusual.