One of the hallmarks of serial killers is their above average IQ's.
The chrisma thing is kind of interesting - in daily life they tend to be loners. Not very social, but not anti-social. When approaching their victims or targets they can be extremely persuasive?
Male, caucasian, 25-35, underachiever, steady employment, single, few relatives with geographical proximity. That is the broad description of 80-90% of serial killers.
I loved Maerdywn's chilly description.
[EDIT]: 1 last thought - most of them have sick names like creamsteak. For some reason that word turns my stomach. Very original
Thanks, Eosin
After posting that, I decided that this serial killer had to make an appearance in my campaign - Hope that's okay with you, creamsteak...