I used to study serial killers fanatically...
My book collection is full of books based on killers. Just the fact that so many people were killed and it was occasionally spread out (time wise), it would stop, and then happen again (leading cops to beleive there were copycats)...I just can't believe that it was one "slick" person. I obviously have no hard evidence, it is just my conclusion/theory. I also believe that it may have been a scapegoat for unsolved murders at the time. "Oh, it must have been the Zodiak Killer". Some of the murders they poitned on him/her/them were just random murders, but that is really what defines a serial killer. Multiple murders, one being unrelated to the next. The killer(s) is supposedly from Northern California, but they pin murders on the Zodiac that happened in Southern. So this guy drove up and down California murdering people? Possible, ut doubtful to me.
I was never a fan of the Zodiak Killer(s), nor Manson (even though he wasn't a killer), nor Jack The Ripper, etc.
Ed Gein, Edmund Kemper, Albert Fish (even though he was truely sick) interested me more than the mainstream killers. That's off-topic though...
Chikatilo was probably the most deranged, in my opinion, next to Albert Fish.