A university student who murdered his housemate in a “carefully planned and cold-blooded execution” outside their house has been jailed for a minimum of 28 years.

Zack Coughlan, 23, dressed all in black and wore a ski mask and gloves to ambush robotics student Jamie Collins, 21, in the garden of their home in Filton, South Gloucester, on 8 April.

Bristol Crown Court heard that Mr Collins was stabbed 30 times before Coughlan left him dying in the alleyway, then cycled away on his bike to dispose of bloodstained clothing and the knife used in the attack.

Coughlan had denied murder but changed his plea to guilty ahead of the jury retiring to consider their verdict in the case, after the trial judge ruled the defence of manslaughter by loss of control was not applicable.

Mr Justice Linden jailed the defendant – who is half Danish and grew up with his family in Cork, Ireland – for life, and ordered him to serve a minimum of 28 years in prison.

The judge told him: “Mr Collins was a fellow student of yours, in the final year of the robotics degree course.

“Mr Collins was an idealist who took an interest in the problems of the world and of society.

“His friends were unanimous in describing him as an exceptionally kind and considerate person.

“It is clear that they felt privileged to have known him and heartbroken to have lost him.”

The judge referred to the impact of Mr Collins’ death on his family.

“The emotional scars that you have inflicted on them will never be fully healed and sadly nothing this court can say or do will turn the clock back,” he said.

Mr Justice Linden told how Adam Vaitilingam KC, prosecuting, had called the killing “a carefully planned and cold-blooded execution”, and said he agreed with this description.

The court heard Coughlan had planned Mr Collins’ murder for weeks, purchasing black clothing and shoes on 27 March and making internet searches on his phone such as “what corpse looks like”.

On the day of the killing, he went into a nearby alleyway and changed into the black clothing to disguise himself.

Coughlan then lay in wait for Mr Collins to return back from university for more than 20 minutes, before launching a ferocious attack as he opened their garden gate shortly before 6pm.

The attack was captured on a CCTV camera installed at the property by Coughlan.

“The injuries which you inflicted were unsurvivable and, perhaps mercifully, it would not have taken long for Mr Collins to die,” the judge said.

The defendant used Mr Collins’ bike to cycle away from the scene, leaving it at a nearby retail park before walking to a duck pond and throwing his bloodstained clothing – in carrier bags weighed down with bricks – into the water.

Coughlan returned to the three-bedroomed home he owned in Cleve Road at about 9pm, put a pizza in the oven and did some online gaming with friends.

It was not until just after 2am that Coughlan dialled 999, claiming he had just found Mr Collins’ body in the rear garden.

“Your callous behaviour continued as you then lied to the police in a calculating, cynical and manipulating way,” the judge said.

A post-mortem examination found that Mr Collins, from Swansea, south Wales, had suffered more than 30 stab wounds to his front, back and neck.

The judge told Coughlan: “We will never know precisely why you killed Mr Collins.”

He rejected assertions by Coughlan in evidence that Mr Collins had expressed violent sentiment about highly wealthy individuals and said he wanted to kill the defendant.

“The evidence is that he was a gentle soul,” the judge added.

“What came across from your evidence as a whole was that over time, you had become deeply upset by the realisation that Mr Collins disliked you.”

During the trial, Coughlan claimed he had killed Mr Collins after feeling threatened when the student expressed left-wing views, which were anti-capitalist and anti-landlord, and became angry about being charged rent by him.

However, in a victim personal statement read to the court, Mr Collins’ family described Coughlan’s evidence as “excruciating” and “full of lies”.

They said his claims were an attempt to “discredit and defame Jamie’s excellent character”.

“I believe Zack Coughlan did feel threatened by Jamie,” the statement by his stepmother Lisa Collins added.

“Not because Jamie ever threatened him, but because of Zack Coughlan’s own insecurities and the reality that Zack Coughlan’s friends were gravitating more towards Jamie.”

Mrs Collins added that the loss of control in the case was Coughlan’s “control over his peer group and perceived popularity”.

“Zack Coughlan knew that Jamie was a better person than him,” she said.

“Zack Coughlan was jealous of Jamie’s integrity and strength.”

She described the devastating impact of Mr Collins’ death on his family and friends, many of whom attended every day of the trial.

The court heard Mr Collins had almost completed his degree at UWE Bristol, with only two further pieces of coursework to finish before he planned to return home to Swansea at the end of April.

His family attended his graduation ceremony, where Mr Collins had accumulated enough results to be awarded a 2:1 degree.

Dan Pawson-Pounds KC, representing Coughlan, said his client had no previous convictions and friends had been “utterly shocked” by his actions.

“He was someone who was well thought of within the peer group,” Mr Pawson-Pounds added.

The barrister referred to Coughlan’s difficult background, which the defendant said in evidence included physical violence from his father and his mother often working away for her job at Apple.