Tristan Roberts appeared remarkably calm when police arrested him outside his Prestatyn home after his mother, teaching assistant Angela Shellis, was found dead in woodland near a nature reserve.

The 18-year-old was handcuffed by North Wales Police at around 1.20pm in October 2025, hours after dog walkers discovered Ms Shellis, 45, lying in undergrowth beside a footpath at Morfa Nature Park.

Roberts was later convicted of murdering his mother and sentenced at Mold Crown Court in March to a minimum of 22 and a half years in prison.

His arrest, the investigation that followed and the evidence eventually presented in court feature in a new episode of Channel 4’s 999: What Happened Next, airing on Mondays at 9pm.

Roberts calmly walked out of his home

Footage from the programme shows officers approaching Roberts outside his house and instructing him to turn around and face a wall.

One officer then asked him to drop the water bottle he was carrying before telling him: “Just going to put you in handcuffs for now, okay? Have you got anything on you?”

Roberts replied: “No. Am I detained or arrested?”

Police told him that officers had seen him come to the door and come outside, and that they would wait for additional officers before entering the property.

Detective Constable Claire Owen, who worked on the investigation, recalled that Roberts came out of the house calmly and allowed himself to be handcuffed.

At first, officers considered whether he might have been in shock or simply did not understand the seriousness of what was happening.

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

DC Owen said his reaction appeared unusual given that he had just been arrested on suspicion of murdering his mother.

Police were first called after a dog walker found a body

The investigation began at around 8.30am, when a dog walker contacted 999 after discovering a woman’s body hidden in undergrowth beside a gravel path.

There was also a substantial trail of blood leading along the path.

Officers secured the area and brought in drones as they began searching the surrounding nature reserve.

Among the items discovered at the scene were a crutch, a balaclava and a pair of black gloves. At that stage, however, police did not know the identity of the woman.

That changed shortly after 1pm when a relative of Angela Shellis contacted police with concerns about both her and Roberts.

Family members had become worried after Roberts barricaded himself inside the home.

Police were told that Shellis had been using a crutch because of a knee injury, prompting officers to focus their attention on the family property.

CCTV placed mother and son together in the early hours

Investigators obtained CCTV footage showing Roberts and his mother leaving the house at around 3.20am.

Roberts was carrying a rucksack, while Shellis was using her crutch.

The footage became an important part of the investigation and led police to arrest Roberts.

However, detectives initially kept an open mind about what had happened after the pair left the property.

DC Owen explained that officers strongly suspected Roberts, but still had to establish whether he had left his mother at the nature reserve and whether someone else could subsequently have been responsible for her death.

Detective Superintendent Andy Gibson, the senior investigating officer, said investigators still needed to answer crucial questions about Roberts’ movements, whether he was responsible for the killing and what had motivated the attack.

Further CCTV footage showed Shellis and her son crossing a local railway line and continuing towards the Morfa site.

Roberts later returned home alone.

He then left the property again, following the same route but carrying a bag. Investigators believed it contained bleach and other liquids that could have been used to clean the scene.

A hammer was subsequently found inside Roberts’ home, in a carrier bag.

Police uncovered disturbing online material

As detectives continued building their case, they examined Roberts’ online activity in the months leading up to his mother’s death.

According to the investigation, Roberts had posted material expressing hatred towards women and had discussed killing people.

One message reportedly read: “I do hate girls, are you OK with that?”

Investigators also discovered that an AI tool had advised him that a hammer could be used as a murder weapon by an inexperienced killer and had provided information about cleaning up after a killing.

Roberts had previously been diagnosed with autism and ADHD.

Police also found messages that appeared to show planning and an intention to carry out violence before Shellis was killed.

His brother had tried to make sure their mother was alive

The family had become concerned about Shellis on the day of her death.

Her older son, Ethan, had messaged his mother after she failed to answer her phone.

“Just call me for a second – so that I know you are alive,” he wrote.

Roberts then allegedly responded while posing as his mother, writing: “I think I am alive [laughing emoji].”

After Shellis was killed, Roberts also posted online about what had happened, describing it as “the craziest day” and making claims about having beaten his mother and smashed her skull with a sledgehammer.

The messages became part of the evidence examined by investigators.

Angela Shellis was remembered as a devoted mother

While the police investigation focused on reconstructing the final hours of Shellis’ life, a family liaison officer was assigned to support her relatives.

The officer, who cannot be named for operational reasons, described Shellis as a mother, daughter and sister who came from a close-knit family.

She was said to have been particularly devoted to her two sons and to have done everything she could to support them.

The family liaison officer also said relatives were aware of the difficulties Shellis had faced in trying to ensure Roberts received appropriate support and accepted that support, while his behaviour had deteriorated.

Shellis’ sister, Sarah Gunther, later spoke in court about the woman she wanted her sister to be remembered as.

She described Angela as “a mum who never gave up, no matter what life threw at her”.

She also said the family had “fought so hard” in an effort to get Roberts the help they believed he needed.

Roberts was sentenced to at least 22 and a half years

The investigation ultimately led to Roberts being convicted of his mother’s murder.

He was sentenced at Mold Crown Court in March to a minimum term of 22 and a half years in prison.

The new 999: What Happened Next documentary revisits the police response, the evidence that led investigators to Roberts and the events surrounding his arrest.

For Shellis’ family, however, the case remains the story of a mother whose life ended in a violent attack and relatives who had spent years trying to support her son.

Sarah Gunther’s words in court reflected that loss, as she asked that Angela be remembered above all as a mother who continued trying to help her family despite everything she faced.