Note: contains discussion of themes that some readers may find upsetting.
BBC drama Four Lives tells the story of four young men who were murdered in Barking, London, back in 2014 and 2015.
Anthony Walgate, 23, Gabriel Kovari, 22, Daniel Whitworth, 21 and Jack Taylor, 25, had first started talking to Stephen Port on dating apps before visiting his flat, where they were drugged, sexually assaulted and killed.
Walgate's body was discovered right outside Port's home, while Kovari and Whitworth were discovered in the graveyard of a nearby church. Taylor was found a short distance from that location.
The three-part series, which was originally named The Barking Murders, is told from the perspectives of the families and friends of the four men, who fought ceaselessly to uncover the truth in the face of a police investigation which was littered with mistakes.
The families of the victims called it "one of the most widespread institutional failures in modern history" after an inquest concluded that errors made by the Metropolitan Police following Walgate's murder "probably" contributed to the deaths of Port's other victims.
Stephen Merchant, who was cast as Port in the true-crime drama, acknowledged to RadioTimes.com and other press that the role is a departure from what he's used to, before going on to discuss how he approached playing the serial killer.
"I didn't meet Stephen Port," he said. "He’s in jail and I have no particular interest in meeting him. I didn’t meet people that knew him either, [including Port's neighbour and friend Ryan Edwards, who visited the set].
"I think I felt I needed to keep some distance from it, in part because of what [executive producer] Jeff [Pope] said about not trying to editorialise too much. When you meet people that know a subject like that, they obviously have their interpretation of that person, their experience of that person, and I was concerned it would skew me in one direction or another.
"The only thing I really had to draw on initially was the police footage of his interviews, which are available. And that gives you a sense of him in those circumstances, which are obviously quite unique because he's being interviewed about crimes. But it gives you a certain sense of his kind of body language and his speech rhythms and so on. "
Merchant also went on to discuss how he personally found the experience of playing Port, who received a life sentence with a whole-life order in November 2016.
"It was a challenge, an enormous challenge," he admitted. "I think had Port been the very centre of the drama, I might have been more trepidatious about trying to shoulder three parts like that. But I think the fact that he is this not peripheral, but a sort of secondary character in a sense, and we're not trying to fully understand him; he is a shark prowling the waters.
"I felt like what I needed to do was to construct my own interpretation of my own internal logic about how someone like that thinks. They know they've killed four men, but they're not going to admit it. So do they know they're lying? Or have they constructed a reality that they're now living by? Are they navigating their way between truth and lies?
"And so a lot of the work I was doing was almost like a writer trying to write in my own head. What is this person's inner thoughts in those moments? Because otherwise you're sort of a bit at sea.
"I also felt the story itself was just so, so important to tell. The idea that in 2014-15, you're still coming up against silence [with the police]; you still can't get through the door when you're trying to help. You're not even trying to obstruct, you're trying to help. You're saying, 'Let me ask questions. Let me see the forged letter [placed by Port] that was found on one of the victims.' That is what I just found so utterly shocking, and why I felt it was an important piece of work.'
Four Lives will air over three consecutive nights on Monday 3rd January at 9pm on BBC One, with all episodes on BBC iPlayer from the same time. Looking for something else to watch? Check out our TV Guide.