Journalist Bob Cyphers on the decades-long search for the unidentified serial killer and what's made the process of identifying him so hard.

Before they're caught, serial killers often fly under-the-radar. But just because police and the public aren't aware of a killing spree, doesn't mean it isn't happening. We look at five unsolved serial killer cases, the murders connected to them and some of the information we do (and don't) know.