The first episode of three-part drama Des aired last night (Monday 14 September) on ITV, and went down a storm with viewers, as many praised David Tennant's chilling portrayal of serial killer Dennis Nilsen.
However, one character in the real life story got closer than most to Nilsen - Detective Chief Inspector Peter Jay, the police officer who arrested him.
DCI Jay, played by Line of Duty's Danny Mays in the show, was not only crucial in the conviction of the killer, but he also managed to extract the most gruesome details of the killings from Nilsen.
The necrophile grew to trust DCI Jay, and told him how he would invite homeless men and teenage boys back to his London home, before strangling them.
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He explained at the time how he'd sometimes dress up the bodies up, before chopping them up. Some of the parts he would store under his floorboards, leaving them to the decayed; others, he flushed away - which ultimately led to his downfall, as body parts were found in the drains.
DCI Jay, from Hertfordshire, passed away in 2018, but his son Simon, 32 - who has a supporting role in the drama - said that his dad had a unique relationship with Nilsen, adding that the killer seemed to genuinely trust him.
Speaking to LADbible, Simon explained: "My Dad was the DCI who led the investigation. He and his team were tasked with convicting a serial killer who had admitted to the crimes before they had any real evidence identifying a body.
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"They didn't know what the truth was, they had no computerised equipment to use, and the killer had no idea who the victims were. It's a very unique case in that respect."
Nilsen was eventually convicted of murdered at least twelve young men and boys between 1978 and 1983 in London, with DCI Jay at the forefront of the case.
"He always told me [Nilsen] was just a strange person," Simon explained.
"He didn't think he was mentally unwell, as Nilsen tried to claim (for diminished responsibility purposes).
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"Nilsen loved the power, the control - So anyone who was hanging on to every word he said would continue to be spoken to. He was a true narcissist in that regard. To get what you want from him, you had to play him at his own game.
"Nilsen wrote several private letters to my father which I still have, and it's quite clear Nilsen trusted my Dad, despite him being the man that was convicting him to life in prison."
Simon, who was born in 1988 - just after the case had ended - was always told stories about his dad's ordeal with Nilsen, but never in as much detail as the TV series depicts.
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He continued: "I've seen all three episodes, they're absolutely brilliant. The acting is superb.
"David Tennant is absolutely chilling as Nilsen. The tiny mannerisms him and Danny [Mays], who plays my Dad, have been consistent with really do bring it to life.
"I can't say I didn't have a tear in my eye on a few occasions; It was just so strange watching someone who looks like my dad, acting like my dad would've, for millions to see. Very weird!"
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Simon, rightly so, is extremely proud of his dad's legacy, saying the production team have done a great job of making sure his dad and Nilsen were depicted accurately.
He added: "Obviously it is a drama, so there are some scenes where Dad may have reacted in less of a shocked manner and more assertive than how it is portrayed in the drama, but the reactions need to be there in the programme so the audience understands what is going on.
"The actual events, the way Dad reacts with his team and speaks to them all etc, is spot on. Dad always had a very cool head but was very assertive (as his police reports say). Danny has his mannerisms down to a tee. It's incredible to watch."
Sadly DCI Jay passed away in February 2018 from cancer - just a month before the production company got in touch with the family about creating Des. But his dedication to helping others lives on.
He helped to set up a charity helpline for people with skin cancer, Sarcoma UK, and also passed on his passion for fundraising and giving back to Simon.
Simon is now keen to help police officers with mental health issues and has set up a charity called Police Treatment Centres.
He said: "The PTC is an independent charity set up to support our police officers who are severely injured either physically or mentally in the line of duty. They save the lives of those who have risked theirs to protect ours, to put it bluntly.
"On 4 October I'm running the 40th London Virtual Marathon across Hertfordshire, raising money for the PTC."
If you are in a position to help, you can donate to Simon's Just Giving page here.
Featured Image Credit: ITV/Simon JayTopics: UK News, TV and Film, UK Entertainment, ITV