I've read a lot of true crime books on serial killers and quite few (particular those by Jack Olsen) have sections where the writer has interviewed hookers, if its a killer who goes after them primarily, and they always talk about how they have all types of clients including a lot of cops. I remember one story about a woman who said she was constantly harassed by one cop for free sex so she won't be taken in. shyt most likely happens all the time.