The father of 22-year-old incel killer Jake Davison has told Ross Kemp's new documentary that he's still trying to understand his son's 'senseless' actions.
On August 12, 2021, Davison killed his mother Maxine, aged 51, following a row at their home, before shooting dead four others - including three-year-old Sophie Martyn - during a 12-minute attack in Keyham, Plymouth.
The mass murderer, who shot himself dead as police arrived, frequently posted misogynistic rants on YouTube after being influenced by incel - or involuntarily celibate - subculture.
His father Mark Davison knew nothing of his 'shy' son's woman-hating beliefs, he told Crime+Investigation in a new series called Lost Boys, Deadly Men, which premiered on Monday.
'Jake never spoke to me about resentment of women, and it's only because he had a picture on his bedroom wall of some young model in a bikini that I knew that he was heterosexual.'
Nearly five years later, Mark has more questions than answers as he tries to reconcile what he knew of his 'bubbly and fun' son with the 'incel' gunman who carried out one of the deadliest mass shootings the UK has ever seen.
Davison was a baby when his mother, cancer survivor Maxine, separated from Mark and the pair moved into a house on Biddick Drive in the Keyham area of Devon city.
According to Mark, they 'argued for years' even though they 'went everywhere together', as he said: 'Familiarity breeds contempt.'
Mark remembered Davison as being quiet and reserved, adding: 'When he was a little lad, he was all bubbly and fun. As he got older, he just got more introverted.'
He recalled how Davison went quiet and 'said nothing' when Mark asked him if he had a girlfriend during a visit to Biddick Drive before Maxine urgently shut down the conversation.
'I thought he was just a bit shy,' Mark said.
What was lurking under the surface was far more sinister, as Davison had been exposed to incel chatrooms and social media groups.
The father of 22-year-old incel killer Jake Davison has told Ross Kemp's new documentary that he's still trying to understand his son's 'senseless' actions
In its simplest form, an incel or involuntary celibate refers to someone unable to find a romantic or sexual partner despite wanting one.
But, in recent years, a more radicalised sub-culture of incels has formed online, characterised by an extreme hatred for women due to intense feelings of sexual frustration.
Davison raged about his inability to find a girlfriend while also lashing out at 'simple-minded' women who are 'biologically set up to care more about looks' in videos posted to his YouTube channel that have since been taken down.
In one video, Davison spoke about his inability to 'meet girls' because he worked in a 'male environment'.
In another, he referred to himself as an 'incel' as Davison said: 'Imagine failing at everything in life and having absolutely no support whatsoever.'
He also posted 'hate-filled online rants' about single mothers - including his own - and described Maxine as a 'vile, dysfunctional, chaotic mother' in posts on Reddit.
But signs of his anger towards his own 'subhuman' life and Maxine, who encouraged Jake to seek mental health treatment, soon bled into real life.
'Over the years, as I visited the house, there would be holes punched into doors, and it wasn't like I could take Jake aside and say 'What's happening, Jake? Are you alright?" because he wouldn't talk to me,' Mark said remorsefully.
'Whatever was going on in that house, it was obvious the last thing you wanted to bring into that environment was a 12-bore pump-action shotgun.'
Mark was referring to the murder weapon that was pictured shortly after the deaths of Maxine, three-year-old Sophie Martyn, her father Lee, 43, Stephen Washington, 59, and Kate Shepherd, 66, on August 12, 2021.
On August 12, 2021, 'incel' gunman Davison killed his mother Maxine, aged 51, following a row at their home, before shooting dead four others - including three-year-old Sophie Martyn - during a 12-minute attack in Keyham, Plymouth.
The case sparked widespread outrage after it emerged Davison had been granted a firearm license despite having a history of mental health issues and violence.
At an inquest hearing in January 2023, it was revealed that Davison declared he had been diagnosed with autism on his application in 2017, before Devon and Cornwall Police issued a certificate in January 2018.
Davison's gun was seized, and his license revoked, after he assaulted two teenagers in 2020.
However, the weapon was handed back to Davison in July 2021 after he completed a police-endorsed rehabilitation program.
Weeks later, he used the same gun to shoot Maxine at their home on Biddick Drive before murdering Sophie Martyn, three, and her father Lee, 43.
Sophie and Lee, who died protecting his adoptive daughter, were shot dead in front of horrified onlookers as they walked their pet dog.
Davison then shot Stephen Washington, 59, in a nearby park, before shooting Kate Shepherd, 66.
Jake turned the gun on himself before armed police arrived on the scene.
Mark became emotional as he recalled the moment he arrived at Biddick Drive, cordoned off and swarming with police cars.
'There was a good part of me shouting, "I told you so, you just wouldn't listen to me,' Mark said. 'You should never have given him the shotgun in the first place.
'Everybody would have still been alive. Jake would have been alive, his mum, that little girl...' he said, his voice trailing off.
Mark previously told the inquest in January 2023 that he had tried to stop his son from getting hold of a gun, including warning police not to grant his firearms licence four years before the shooting.
Lost Boys, Deadly Men hopes to continue the conversation sparked by Netflix's Adolescence, which was released last year. It follows 13-year-old Jamie Miller (played by breakout star Owen Cooper) after he is arrested and charged with murdering a female classmate.
'With violent crime against women on the rise in Britain by young men, Ross Kemp wants to find out what can be done to stop it.'
The first episode, which was released today, revisits the horrific 2021 Plymouth killings by 'Britain's incel killer' Davison.
New episodes are released on Crime+Investigation every Monday.