oh, this thread is a good one to make the requisite karla homolka mention. if you dont know her story, her and her husband were considered the Barbie and Ken killers in Canada in the 90s.
she is an example of a hot, but complete nutjob, fascinated by and falling in lover with a demented killer, paul bernardo
Notice they look like your normal looking couple...
homolka:
http://www.trutv.com/library/crime/serial_killers/notorious/bernardo/index_1.html
Google results: