ITV's The Confession, tells the story of how Detective Superintendent Steve Fulcher breached protocols to catch a killer.
His story is a true story, and one which has fixated the imagination of audiences across the country.
Christopher Halliwell has since been sentenced for murdering 22-year-old Sian O'Callaghan, and 20-year-old Becky Godden-Edwards.
Martin Freeman, who plays Det Supt Fulcher, says getting into the mindset of the detective was not a difficult task.
Controversy surrounds Det Supt Fulcher's decision not to read Halliwell his rights, or provide him with a lawyer and bring him to a police station, when he was arrested.
Instead the detective said he wanted to speak with Halliwell ‘man-to-man', and use emergency powers - as he believed there was an imminent threat to life.
But, Fulcher had not cautioned Halliwell as he should have under the Police and Criminal Evidence Act (PACE).
There have always been questions around whether Det Supt Fulcher's gamble to persuade a serial killer to admit murdering two women, was brilliant policing, or totally illegal.
But although the monumental gamble secured the admissions, it also led to the detective's own downfall.
He didn’t take Christopher Halliwell into a room and kick him. He didn’t frame him up. He didn’t put words in his mouth. If no-one told a civilian that those rules had been breached, we would never know why they were breached. Because it looks reasonable.
Freeman added as he was preparing to play the role he was struck by Det Supt Fulcher's professionalism, and said he believed he was "not a push-over in any way".
He added: "He struck me as very professional, very high standards, and not a push-over in any way. And probably someone who could drive you mad, actually. I don’t think he would ever say ‘that’ll be fine, that’ll do,’ he struck me as someone who would say ‘this will be done the right way’ ironically, given his decisions breached PACE.
“He couldn’t have seen what would happen to him. But I certainly don’t think he was going to get any commendations or pats on the back for doing it. It felt to me that he was trying to do the right thing to find a woman who has been missing. Maybe that’s me being naïve. I totally believe in his motivations."
The actor also said he felt sorry for the detective, who had to slowly watch his "reputation and livelihood slipping away".
“The decision he made may have been wrong, that’s not for me to say. But you’d be hard-pushed to find someone who would sat it was an awful, terrible, immoral decision. To lose as much as he’s lost for that is harsh,” he said.
- WATCH: A Confession: as told by ITV News. The real story behind the drama as caught by our cameras.