In the upcoming film The River Murders, Ray Liotta plays a police officer who may or may not be a serial killer. As you may already know, the cop-who-may-be-a-serial-killer character is a well-established tradition in movies. To prove that, here are six movie cops who might also be serial killers.

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Lou Ford, The Killer Inside Me

Remember that thing about how the cops on this list might be serial killers? Well, in Lou's case, you can go ahead and change that to "definitely is a serial killer." Ford is a small-town sheriff played by Casey Affleck who manages to hide his murderous tendencies from everyone around him. Basically, he kills people because he enjoys it. If you ever get pulled over by this guy for speeding or something, don't try and get out of it - just pay the fine.

Hank Quinlan, Touch of Evil

Captain Hank Quinlan, an officer of the law in one of America's seediest border towns, was a great detective. And a lousy cop. And he always gets his man - if not through the proper channels, than by any means necessary. Evidence planting, intimidation, extortion, and even murder are all at the disposal of Quinlan, as played by Orson Welles who also directed the 1958 noir masterpiece. Not that difficult to imagine him committing a series of murders if he thought it was necessary to an investigation.

Alonzo Harris, Training Day

This cop, famously portrayed by Denzel Washington is similar to Captain Quinlan in terms of tactics and what he's willing to do to crack a case. In a way, he's even more corrupt than Quinlan, since he's also in the drug dealing game, using his badge and gun for fun and profit. But he's also a little bit crazy. If he hadn't run afoul of those Russian gangsters, maybe he'd still be killing people at will.

The Lieutenant, Bad Lieutenant

As played by Harvey Keitel in the 1992 film Bad Lieutenant, this unnamed titular character does a lot of bad stuff. He steals drugs, he sexually abuses women, he's violent. Would you be that surprised if he turned out to be a serial killer, too? In Werner Herzog's follow up, Nicolas Cage's take on a similar character is much more deliriously unhinged, so it's even easier to imagine him going off the deep end and storing dead hookers in his freezer.

Steve Burns, Cruising

Sometimes a bad assignment can drive a good cop crazy. That's what might have happened to Steve Burns, who in an unfortunate coincidence happens to resemble several victims of a serial killer who's been stalking the New York gay underground club scene of the late 70s/early 80s. So he has to go undercover in order to catch this guy - but the violent, dangerous world he spends so much time in has its effect on his psyche. By the end of the movie, he not only might be a serial killer, he might even be a gay serial killer. Hope his girlfriend's cool with it.

"Dirty" Harry Callahan, Dirty Harry

Now, now, don't start freaking out on me. I know that Clint Eastwood as Dirty Harry is one of the most revered heroes in recent movie history, and I know he never killed anybody who didn't "have it coming" in one way or another. But consider a tagline for the original 1971 movie: "Dirty Harry and the homicidal maniac. Harry's the one with the badge." When you get right down to it, maybe Harry's violent nature brings him closer to the serial killers, creeps, and scumbags he stalks than he realizes.