A group of Rimutaka inmates attacked and knocked unconscious another prisoner who they thought had "narked" to prison guards, a court was told today.

Prison guards trying to protect the prisoner were also attacked, with one being struck with a roundhouse kick to the head, Crown prosecutor Geraldine Kelly told a jury.

The trial began this morning at Wellington District Court for three inmates who were allegedly involved in the pack attack against fellow inmate Anton Matenga two years ago.

Arthur Briggs, Regan Cross, and Elise Tuese each face one charge of injuring with intent to injure.


Briggs is also facing one charge of injuring with intent to cause grievous bodily harm.

Two others, Hamiora Moke and Brock Norton earlier pleaded guilty to related charges.

Yesterday, Briggs pleaded guilty to four charges relating to assaults against the prison guards at the incident.

Ms Kelly told the jury of four women and eight men that the defendants, Moke and Norton went to Matenga's cell on the morning of June 1, 2012 after a hit had been put on him for narking to Correction Department officers.

Norton stayed outside the cell as a lookout, while the four others went in and closed the door, she said.

The group then pushed Matenga face down onto the bed and attacked him until Norton alerted them that guards were coming, Ms Kelly said.

Matenga did not know who had punched and kicked him.

Guards, including officer Tom Dixon, went into the room, at which point Briggs said "let's go all out", before Briggs jumped on and stomped on Matenga, knocking him unconscious, Ms Kelly said.

"After he did this he did a roundhouse kick to Tom Dixon's head."

Briggs then continued his attack on Mr Dixon, and kicked him into unconsciousness while he lay on the floor, Ms Kelly said.

She said the guard suffered from an ongoing brain injury.

Several guards were attacked during the incident before all men were subdued, she said.

The Crown can not say exactly who did what to Mr Matenga.

"But they all went into that room and they closed the door and they had a lookout."

Briggs' lawyer Geoff Fulton told the jury his client had pleaded guilty to the actions he was responsible for.

He asked them to keep an open mind about the case.

Paul Surridge, appearing for Cross, said his client was only 18 at the time of the incident, "a lad" who found himself in the cell while the beating was taking place.

He was only in the area because he was visiting Moke to ask for some moisturiser for a skin ailment, Mr Surridge said.

Cross had just six days until a parole hearing and did not want to be involved in any trouble, he said.

Tuese's lawyer, Liz Hall, said her client was in a similar position, with only two weeks before the end of his sentence.

She said he was in Matenga's cell to say "gidday" to him when the others came in and the door was closed.

"He didn't touch Mr Matenga at all."

The trial, in front of Judge Jan Kelly is set down for the week.