In real life, someone like Dexter wouldn't even be fully noticed until someone found some of the bodies and made the link. I mean, Ted Bundy got away with what he did for a long time because he was someone nobody could ever suspect of being a murderer. He was charming, good-looking and friendly, and even police WERE tipped off about him they ignored it because they didn't think someone like him was a murderer.
In what I've seen of the series, he targeted criminals, several of whom were black so the police probably wouldn't care too much unless somebody kicked up a stink about it (There is, in fact, a serial killer currently at large in LA who preys upon black women, and who has had little done about him. Google the Grim Sleeper.) He'd get caught in the end, for sure, but it would take a while, I think.