You might have had a sneaking admiration for Dr Hannibal Lecter’s insistence on fresh produce, or even Charles Manson’s taste in music, but there has never really been a serial killer you’d want to spend quality time with . . . before Dexter Morgan. Sure, he’s a ruthless, cold-eyed murderer with a penchant for clingfilm and garottes, but he’s a murderer with scruples. His foster father, a policeman, saw early that his boy had a vicious bloodlust, so he took it upon himself to channel Dexter’s interest into a force for good. Now that Dexter is a member of the police himself, in forensics, he uses dad’s training to target “bad” serial killers who are duly done by as they have done.

The upshot is that Dexter, whose second series begins this week, exists in a moral maze as easily navigable as the Bermuda Triangle – you end up rooting for the sociopath with the power drill ahead of almost everyone else. We spoke to Michael C. Hall, who plays Dexter, to try to unscramble his warped psyche.

He has a code

The Code of Harry, left to Dexter by his foster father, is pretty simple as criminal ideologies go – first, make sure your scumbag is indeed a scumbag. Then make sure you don’t get caught. In season one, Dexter was slaying away quite happily with only his boorish colleague Doakes smelling the slightest semblance of a rat, but in season two the FBI catches up. “The heat is being turned up and there’s a possibility of his being found out,” Hall says.

And he has a method

Once Dexter has worked out that someone deserves dispatch, he picks a quiet spot and injects them with animal tranquilliser. Hall, somewhat spookily, claims to have almost gone method in preparation for the role: “I followed some strangers around and endowed them with reprehensible characteristics to see how that would feel.” In the fiction, when Dexter’s victims come round, they are covered in clingfilm, strapped naked to a table. He confronts them with their crimes and chops them to bits with a battery saw, wrapping up the body parts in bin bags and dumping them in the ocean. In the new series, we’ll find out where – as will several others.

He feels no human emotion

Dexter says he has no conscience about his kills, no compassion or genuine affection in his life. But it doesn’t quite wash, and in season two we’ll see a little more of what could be humanity. “Dexter has a sort of childlike approach to life,” Hall says. “He plays at life but he’s much more susceptible to standard human vulnerabilities than he believes. Season one asked, ‘What makes Dexter do what he does?’ The second season is maybe more, ‘What am I? Am I good, or am I evil?’ He goes out with a multiple rape victim because ‘she’s as damaged as I am’.”

Dexter and Rita have made it through series one intact, and he gets about as close to genuine warmth as he ever does around her kids. For series two, Rita will start to find out more about Dexter’s true nature, via her imprisoned husband (he of the multiple rapes). “I have always been impressed with Dexter’s capacity for stress management,” Hall says, “and that capacity is really taken to new levels in the second season.”

He keeps a record of all of his victims on lab slides

Even an impassive death-machine gets the odd nostalgic twinge. Dexter’s photo album is a spot of blood from each of his victims, always taken by pipette from their deftly slashed cheek, and stored in a display case hidden inside his air conditioner.

Yet he’s the nicest guy around

He brings doughnuts for his coworkers; you’d leave your kids with him . . . “That’s the goal of the show, to make you like him,” Hall says. “He only kills reprehensible people. His honesty, his adherence to his code, as perverse as it might be, is admirable in its way. He’s a very proactive and capable person, a real go-getter! And anyway, we all have our secrets . . .”

Dexter series 2 begins Sun, FX, 10pm

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