i know a bit about psychopaths of course.
most of them are indeed low IQ. them being above IQ like bundy, dahmer, and kemper are pretty rare. in fact, they are pretty much the only ones i can think of. oh, and the unabomber of course.
most of the cannon serial killers were actually fairly dumb. btk, green river killer, gacy - all below average intelligence, gacy approaching average probably.
here's some stats
http://maamodt.asp.radford.edu/Seria...Statistics.pdf