Watch exclusive first-look clip of David Tennant as serial killer Dennis Nilsen in ITV's Des

He adds that the defence does not dispute the killings, only that it claims Nilsen was not of sound mind when he committed the crimes and that he therefore cannot be held accountable.

But he goes on, "I intend to prove that Mr Nilsen not only knew what he was doing, but that these crimes were pre-meditated and carefully planned."

The clip also shows the reactions of Jason Watkins' character Brian Masters - a crime writer who had corresponded with Nilsen and went on to write his biography, and of Daniel Mays as DCI Peter Jay, the police officer who had been in charge of the case.

The three-part series will air on consecutive days next week, with the first episode airing on Monday 14th September at 9pm on ITV.

The series is set in the aftermath of his arrest in 1983 and tells the story of the arrest and trial of the killer, who was known as Des, from the perspective of three different men – Nilsen himself, Jay, and Masters.

This week, David Tennant revealed how he got into character as Dennis Nilsen, telling Radio Times, "There is some footage of Nilsen in an interview he did with Granada Television when he was in prison, and he was an avid home movie-maker, some of which survive, so we were able to see those.

“It was a useful starting point to see how he moved and how he sounded, as there are occasional bits of audio of him around, too. And of course the notebooks – he wrote and wrote and wrote in prison.”

Read the full interview with David Tennant in this week’s Radio Times magazine. Des premieres on ITV at 9pm on Monday 14th September. If you’re looking for something to watch tonight, check out our TV Guide.