investigators to prove that this mysterious conman was also a killer. but was the case as clear-cut as it seemed? >> there was no motive. there was no reason he would have done this. >> for the first time, hear from the detectives who helped crack this puzzling case and from his ex-wife. >> i thought he was very intelligent, funny, very charming. >> for decades, he got away with a web of lies. would he also get away with murder? >> i can fib, certainly, but i have never hurt anyone. >> tonight the mystery of the man with so many faces. i'm lester holt, and this is "dateline," behind ...