Psycho is a great film.

So is North by Northwest and Rear Window and Vertigo. But the greatest of Alfred Hitchcock's films is Frenzy because, more than in any other movie, the great director uses the camera against us: he makes us feel dirty, like a voyeur, or a peeping tom, like the kind of person who might look through a keyhole to see what the neighbours are up to.

But he does something else disturbing in Frenzy as well: he makes us laugh when he shouldn't. He makes us laugh at murder.

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The film, released in 1972, centres on a serial killer who strangles women with a necktie. In its most famous scene, the killer rummages in a sack of potatoes to find a dead body and suddenly her leg, stiff with rigor mortis, springs up and hits him in the face. It's murder as farce; it's death to the soundtrack of our awkward laughter. "Very amusing," Hitchcock called it.

And then, just as you think this is Hitchcock at his most macabre and graphic, he pulls back from the murders. In another of the film's most famous sequences, a woman is murdered but we see nothing. We – and the camera – are on the other side of the door. Slowly, we pull back and head down the stairs, further and further away from the violence. Seconds later we're out in the street and can hear nothing. We walk away.

You can experience all of this squirmy brilliance for yourself when Frenzy is shown at the Filmhouse in Edinburgh from tomorrow but I won't be responsible for how you feel. Five people are murdered in this film and here we are watching it, fascinated, entertained, excited, amused.

That's what Hitchcock does at its greatest and Frenzy is Hitchcock at his greatest: he makes us look at something terrible but also forces us to deal with a difficult, uncomfortable question: why are we looking at this, but more importantly, why are we enjoying it?