Key Points:

The man who today pleaded guilty to the prison-van killing of North Shore teen Liam Ashley said he did it because he thought the 17 year old was a "nark" and was going to give evidence against him.

The 25 year old, who has name suppression, admitted murdering Liam at a packed Auckland District Court hearing this morning.

In a summary of facts read to the court today, Crown prosecutor Simon Moore outlined the events that took place during the last day of Liam's life.

Liam and his killer met at Auckland Central Remand Prison early on the morning of August 24, and were handcuffed together to await transportation to their respective North Shore District Court appearances.

The pair got talking, and it soon transpired that the man's offences were allegedly carried out in an area of the North Shore close to where Liam and his family lived.

The man later came to the conclusion that Liam could give evidence against him at court. His fears appeared to be compounded when he learned from other prisoners being transported that Liam had told them he lived somewhere else.

Later in the day, while being transported back Auckland Central Remand Prison, Liam and the man decided to try to escape the van.

The pair tried unsuccessfully to kick their way out, but then decided that Liam would fake some kind of seizure, to attract the attention of the guards.

When Liam later refused to feign illness, the man attacked him.

The ensuing assault culminated in the strangling Liam for 10 to 15 minutes, before releasing him and stomping up to seven times on his head, the court was told.

When the van arrived back at ACRP about 6pm, Liam was found slumped on the van floor.

The man told told security guards "You better get him out of there, I've just killed him. He's not breathing."

Efforts to revive Liam failed, and his life support system was turned off at 10.45am, next day.

The man, who appeared in court flanked by security guards, was remanded in custody for sentencing in the High Court at Auckland in December. He was granted name suppression as he faces other charges in the High Court.

The man earned public derision at an earlier appearance after appearing in a T-shirt with the words "keep your eyes on the rising star of crime".

But his lawyer Tony Bouchier, outside court, said his client had no idea of the message on the shirt, as it had been given to him by ACRP staff after police took his clothes.

Mr Bouchier also said the man "accepts full responsibility" for his actions, and had written a letter of remorse that would be given to Liam's family and friends.

The man "has never resiled from the truth" of what he had done, and had been co-operative with police throughout, he said.

Liam's parents were also in court for the guilty plea, and later told waiting media it had been "a significant day for the family".

The man's guilty plea had provided a degree of closure for friends and relatives, Liam's father Ian Ashley said.