A university student who lay in wait for his housemate to return home before stabbing him 30 times has been jailed for life with a minimum term of 28 years.

Zack Coughlan, 23, dressed in black and wore a mask and gloves to ambush Jamie Collins, 21, in the garden of their home in Filton, South Gloucestershire.

Bristol crown court heard Collins was stabbed repeatedly and Coughlan left him dying in an alleyway as he cycled away on his housemate's bike.

Coughlan had denied murder and a trial was under way at Bristol crown court but he changed his plea to guilty on Tuesday.

Sentencing Coughlan on Wednesday, Mr Justice Linden said: "He [Collins] was caught totally unaware by you and was utterly defenceless."

He dismissed Coughlan's evidence in court that Collins had previously threatened him, describing Collins as a "gentle soul".

The judge said no one would know why Coughlan killed Collins.

Collins was attacked shortly before 6pm on 8 April this year after cycling home from University of the West of England (UWE) Bristol where he was studying robotics alongside his killer.

Adam Vaitilingam KC, prosecuting, told the jury: "This was a carefully planned and cold-blooded execution."

Coughlan 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.

He returned to the house they shared at about 9pm, put a pizza in the oven and did some online gaming with friends.

At around 2am, Coughlan dialled 999 claiming he had just found Collins's body in the garden.

The attack was caught on CCTV installed at the house they shared, which Coughlan showed the attending police officers who initially treated him as a witness.

The defendant's blood had been found on Collins's bike, and analysis of his mobile phone matched the killer's movements afterwards captured on CCTV.

Coughlan also had injuries to his hands, and he told people who saw him bleeding that he had been climbing trees and had fallen and hurt himself.

After the murder, Coughlan told a university friend he wanted to hold a memorial for his housemate.

Coughlan and Collins, originally from Swansea, were both final year students and lived together in a £300,000 three-bedroom house owned by the defendant.

In a statement issued following Coughlan's change of plea, Collins's family said his death had "affected our family in a deep, profound, and lasting way".

"As a family we have had to explain repeatedly to people what has happened," they said. "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."