Serial killer Ted Bundy had legions of women turning up to his trial, protesting his innocence and sending him love letters. The same goes for Richard Ramirez and Jeffery Dahmer, even though the latter was gay. The public gallery at each of their trials was packed with women giggling, whispering amongst themselves, craning their necks to catch a glimpse of their beloved. Bundy in particular lapped it up, he knew the power he held over them and only had to turn around and flash a smile to stir up a frenzy. One of these so called "groupies" entered into a relationship with Bundy, accepting his marriage proposal when he himself was questioning her as a character witness (his overly inflated ego meant he requested to act as his own attorney, not realising what an utter boob this was). They ended up having a daughter together, although she divorced him in the late 80s.
The psychology behind this is thought to stem from a number of sources - some women think their love can turn the criminal around and that by nurturing them, said person will transform into a caring, compassionate human being, others may be desperate for the 15 minutes of fame that would accompany a relationship with the person and some may see the young child a killer once was. Hybristophilia is a paraphilia whereby an individual becomes attracted to someone based on the fact that they've committed a crime, a fantastical phenomenon often shown by those who struggle to make and maintain romantic relationships in their day-to-day lives.
Obviously Bundy is an extreme example but there are parallels between his case and those of fictional characters.