Moment crazed killer, 18, remains calm as police arrest him outside home for murdering his teaching assistant mother - after keeping her captive then striking her to death with a hammer

This is the moment an 18-year-old son remained strangely calm as he was arrested for murdering his mother hours after dog walkers found her body in undergrowth.Tristan Roberts, of Prestatyn, North Wales, was put in handcuffs by officers outside his home after Angela Shellis, 45, was discovered dead in the Morfa Nature Park.Roberts, who hated women and was obsessed with violence, beat his teaching assistant mother to death in a planned attack with a hammer in October last year.He kept Ms Shellis prisoner in her bedroom, recording her four-hour ordeal before luring her into isolated woodland by pretending he was allowing her to get help.But Roberts then delivered the fatal blows and left her body in the reserve, before returning home around 6.30am – where he was later arrested by North Wales Police.Video footage of his arrest at 1.20pm features in a new episode of Channel 4 documentary '999: What Happened Next', which is airing on Mondays at 9pm.The programme also looks at the evidence that led to him being arrested and his eventual jail sentence of at least 22 and a half years at Mold Crown Court in March.A clip shared with the Daily Mail shows Roberts being told to 'turn around and face the wall' outside his home, before being told to drop a water bottle he is holding. Tristan Roberts, 18, is arrested in Prestatyn in October 2025 after his mother was found dead Angela Shellis, 45, was found dead in undergrowth beside a footpath near a nature reserve Tristan Roberts, 18, was jailed for at least 22 and a half years at Mold Crown Court in MarchThe officer then tells Roberts: 'Just going to put you in handcuffs for now, okay? Have you got anything on you?' Roberts replies: 'No. Am I detained or arrested?'An officer then says: 'All in order at the moment, Tristan came to the door and he came out, so we'll wait for other officers to get here before we go into the address.'Recalling his arrest in the documentary, Detective Constable Claire Owen, who worked on the case, said: 'He came out of the house calmly.'He allowed himself to be handcuffed. Potentially we thought he may have been in shock or very young and didn't understand what was going on. 'She added that Roberts asked officers: 'Is the body that's been found my mum?'DC Owen continued: 'His reaction just seemed very at odds with what you would expect with an 18-year-old who had just been arrested for murder.'The police investigation began earlier that day when a dog walker called 999 at 8.30am, reporting that they had found a woman's body in the undergrowth and a large trail of blood along a gravel path.Detectives secured the scene and deployed drone units. They also found a crutch, balaclava and a pair of black gloves – but did not know the victim's identity at that stage.Then just after 1pm, police received a further call from a relative of Ms Shellis who was raising concerns for both her and Roberts, who had barricaded himself into the home. Roberts answered 'no comment' to questions put to him during subsequent police interviewsThe hammer found at Roberts's home in Prestatyn, which he had earlier bought on Amazon Police found a pair of black gloves at the murder scene beside a footpath near a nature reservePolice were told Ms Shellis had been using a crutch because of a knee injury – and headed to the home, by which time family members had managed to get inside.During that period officers also obtained CCTV of Roberts and Ms Shellis leaving the home at 3.20am, with Roberts carrying a rucksack and Ms Shellis with a crutch.Police thought this was significant enough to arrest Roberts, which they did – and detectives then worked to establish his exact movements.DC Owen said: 'We had to keep an open mind as to who committed this offence. We strongly suspected Tristan at that point, but equally it's possible that he'd left Angela in the nature reserve and someone else had done this.'Detective Superintendent Andy Gibson, the senior investigating officer, added: 'So at this point in time we've got CCTV evidence of Tristan's movements.'But we still need to fill evidential gaps. Was he responsible for the murder of his mother? What was the motivation in terms of that murder?'Investigators then found footage of the mother and son going over the local railway crossing, heading towards the Morfa site – before Roberts returned to the home.Soon after that Roberts left the home alone again, following the same direction but this time carrying a bag – believed to have bleach and other fluids to forensically clean the scene. The contents of a carrier bag found inside Roberts's home address, including a hammer Roberts shared messages about hating women online in the months before the murder Police outside Roberts's home in Prestatyn in October last year following the murderIn the months before the murder, Roberts – who was diagnosed with autism and ADHD - had boasted online about his intention to kill.He also discussed being motivated by a 'hatred of women', writing: 'I do hate girls, are you OK with that?' An AI tool advised him that a hammer would be the best murder weapon for 'a non-experienced killer', and also provided help on how to clean up after the killing.Roberts's older brother Ethan had even texted his mother when she failed to answer the phone on the day of her murder, asking: 'Just call me for a second - so that I know you are alive.'Roberts posed as her, replying: 'I think I am alive [laughing emoji]'.After killing Ms Shellis, Roberts posted online: 'I've just had the craziest day', adding that he had 'beat the s*** out of her' and 'smashed her skull in so hard with a sledgehammer'.On the day of the arrest, a family liaison officer - who cannot be named for police operational reasons – was assigned to support relatives of Ms Shellis.This officer told the documentary: 'Angela was a mother, a daughter herself, she was one of three siblings and she was part of what was a really close family who chose to spend a lot of time together.'She absolutely worshipped both of her sons and did above and beyond what anyone would do for them. She was known as kind and sweet and a lovely person and they all knew each other very well and they all knew Tristan very well.'They all knew the battle Angela was manning to try and make sure that he got the right support and that he took that support - but there was a deterioration in his behaviour.'Ms Shellis's sister Sarah Gunther said in court that she wanted her to be remembered as 'a mum who never gave up, no matter what life threw at her', adding that the family had 'fought so hard' in an attempt to get Roberts 'the help you needed'.'999: What Happened Next' airs on Channel 4 on Mondays at 9pm