An 18-year-old man showed little emotion when police arrested him for murdering his mother, just hours after dog walkers discovered her body hidden in woodland undergrowth.

Tristan Roberts, from Prestatyn in North Wales, was handcuffed outside his home after Angela Shellis, 45, was found dead at Morfa Nature Park.

Roberts, who had expressed hatred towards women and displayed an obsession with violence, killed his mother in a premeditated hammer attack in October last year. Ms Shellis worked as a teaching assistant.

He held her captive in her bedroom and filmed the four-hour ordeal before tricking her into going to secluded woodland, claiming he was giving her the chance to seek help.

Once there, Roberts fatally attacked her and abandoned her body in the nature reserve. He then returned home at about 6.30am, where North Wales Police arrested him several hours later.

Footage of the arrest, which took place at 1.20pm, will feature in a new episode of the Channel 4 documentary 999: What Happened Next, broadcast on Mondays at 9pm.

The programme examines the evidence gathered by detectives and follows the case through to Roberts’ conviction and sentencing at Mold Crown Court, where he was jailed in March for a minimum of 22 and a half years.

A clip shared with Our News Outlet shows officers ordering Roberts to turn around and face a wall before instructing him to put down the water bottle in his hand.

An officer tells Roberts: “Just going to put you in handcuffs for now, okay? Have you got anything on you?” Roberts responds: “No. Am I detained or arrested?”

Another officer explains: “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.”

Detective Constable Claire Owen, who was involved in the investigation, recalled the arrest for the documentary: “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.”

Roberts then asked officers: “Is the body that’s been found my mum?”

DC Owen said his behaviour appeared completely inconsistent with what officers would normally expect from an 18-year-old being arrested on suspicion of murder.

The investigation began at around 8.30am, when a dog walker called 999 after finding a woman’s body concealed in undergrowth. A substantial blood trail was also visible along a nearby gravel path.

Police sealed off the area and sent drone teams above the scene. Investigators also recovered a crutch, a balaclava and black gloves, although the victim had not yet been identified.

Shortly after 1pm, officers received another call from a relative of Ms Shellis, who said they were concerned about both her welfare and Roberts. He had reportedly barricaded himself inside the family home.

Police 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.

In 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