otto - just playing devil's advocate on your last post - Clifford Olson's victims did not have similar characteristics. I don't see the similar characteristics in Robert Picton's or Russell Williams' victims.
There are a lot of unsolved murders and missing people under similar circumstances, imo.
Didn't Clifford Olsen approached young teens, offered them jobs, then alcohol, then drive them to remote areas where he murdered them? IIRC, he went to one mall more than once to meet victims. His ace card was that he picked child up in one district and left them in a different district. Police weren't cooperating with each other, so the murders took longer to solve.