A student who stabbed his housemate more than 30 times in a masked ambush has changed his murder plea to guilty.

Zack Coughlan, 23, attacked Jamie Collins, 21, in an alleyway near the garden of their home on 8 April and then left his body outside for eight hours before calling police.

A murder trial had been under way at Bristol Crown Court because Coughlan initially denied the charge, although he did admit killing Collins. He told jurors he stabbed Collins because he feared his housemate would kill him.

However, Coughlan, of Cleve Road, Filton, has now changed his plea to guilty and will be sentenced for murder on Wednesday.

Describing him as “a sensitive and caring young man”, Collins’ family said he had been “looking forward to finishing his journey” at the University of the West of England (UWE) and returning home to Swansea “in a matter of weeks”.

“His passion for equality stood out to everyone who knew him. His unapologetic inclusivity will be his legacy for all of us. We know he was heading for a hugely successful future following his engineering and robotics degree,” they added.

The men were both final-year robotics students at the UWE and lived together in a house in Filton, owned by Coughlan.

During the trial, Coughlan claimed he was fearful of Collins, telling jurors he was “barely able to think” when he lay in wait for his housemate to return from university before stabbing him repeatedly.

Coughlan then left his housemate to die in the alleyway behind their home before cycling away on the victim’s bike to dispose of bloodstained evidence.

He dumped the bike at a nearby retail park, bought a change of clothes and threw his bloodstained clothing in a pond, in carrier bags weighed down with bricks.

On returning home he ate pizza and played video games, claiming he “had to disconnect” from what happened. He did not call 999 for another five hours.

The entire attack was caught on CCTV Coughlan had installed himself, which also captures the moment he staged the discovery of Collins’ body.

Jurors were told he later rewatched this footage five times.

Det Ch Insp Lucy Edgeworth, of the major crime investigation team, said “all the evidence suggests” the killing was a “pre-planned, cold-blooded execution”.

She said despite Coughlan claiming his housemate’s political views had become more extreme and that he had talked about killing Coughlan, the motive for the murder was “not clear”.

“We know there was a dispute about rent. We know that they held different political views. But none of those things make any sense to why somebody would carry out such a horrific crime,” she said.

Edgeworth pointed out inconsistencies in Coughlan’s story, including claims he had injured his hands climbing a tree after the incident, which she called “slightly odd”.

She added the defendant’s blood had been found on Collins’ recovered bike because he had likely injured himself in the “ferocious and horrendous” attack.

“The retrieval of the clothing from the pond, again, all forensically linked Zach to that crime. So it was a really interesting and complex forensic picture,” she said.

In a statement issued outside court, surrounded by Collins’ family, Edgeworth described the murder as “meticulously planned”.

“The brutal nature of what he did cannot be underestimated,” she said.

“Rather than calling for medical help he did everything to protect himself.

“He feigned shock and the lies continued, both to police and friends in the hours and days after what happened.”

Coughlan changed his plea to guilty after a legal ruling by the trial judge on Tuesday.

Judge Justice Linden said Coughlan’s partial defence of manslaughter by reason of loss of control could not be left to the jury to consider as part of their deliberations on the murder charge.

He told the jury: “You will have just heard that the defendant has changed his plea to the indictment to guilty.

“That means that he now admits the charge of murder.

“I would like, on behalf of us all, to thank you for the service that you have given in this case.”

In a statement issued following the verdict, Collins’ family said his death had affected them in a “deep, profound and lasting way”.

They said: “As a family we have had to explain repeatedly to people what has happened.

“Every time we do so it reinforces the pain of him having been killed so suddenly, and in such a senseless and brutal way.

“Our family has been sickened that Zack Coughlan pretended to help Jamie when in fact he is responsible for killing him.”

They added he had accumulated enough points during his studies that he was posthumously awarded a 2:1 degree in July, which the family accepted on his behalf.

The university described him as a “valued member” of the robotics community and an active member of student societies.

“He was a natural engineer, keen in robotics, a hard worker and only weeks away from completing his degree,” said UWE Bristol vice-chancellor Steve West.

“The details which have emerged during the trial are shocking, and particularly difficult for several of his university friends who were called as witnesses.

“The number of friends and university staff who attended both Jamie’s memorial and the court trial is testament to how much he was cared for.”

Follow BBC Bristol on Facebook, external, X, external and Instagram, external. Send your story ideas to us on email or via WhatsApp on 0800 313 4630.