The killing of retired Opotiki school teacher John Rowe by two teenagers was savage and calculated, a jury in the High Court at Rotorua has been told.

On trial today before a jury of six men and six women are Courtney Pauline Churchward, 18, unemployed, and a 15-year-old girl who have each pleaded not guilty to murdering Mr Rowe at Opotiki on November 25 last year.

Opening the Crown's case, Duncan McWilliam said the teenagers had decided to go into "the old man's house" to rob him.

At the time of his death Mr Rowe was recuperating from an ulcerated leg and was due to return to hospital for further treatment the day after he died.

When the pair arrived at Mr Rowe's home they wore socks over their hands. They covered these with latex gloves which they found in a box in his lounge. These were used by his caregiver when his wounds were dressed.

The teenagers had gone into his bedroom where they attacked him with a wooden broom handle and a walking stick.

In an excerpt from a video interview with police, Churchward said she stood by Mr Rowe's bed for a good two minutes "trying to prepare myself". When she started hitting him he twice tried to get up. She claimed he had still been alive when she left the room.

At the conclusion of the excerpt, Mr McWilliam said Mr Rowe's battered body was found the following morning by a neighbour. It was fully clothed.

Mr Rowe's right foot was on the floor and his left foot over the side of the bed. His face and head were extensively bruised and torn, his left arm broken and the right arm badly damaged. His fingers were torn and broken - injuries consistent with him attempting to ward off blows.

Blood was splattered around his bedroom walls and ceiling and a bedside lamp had been knocked over.

"The Crown says this attack went far beyond subduing this 78-year-old man," Mr McWilliam said.

After the attack Mr Rowe's wallet containing a substantial amount of cash and credit cards, and a radio-CD player were stolen. The wallet was subsequently found discarded in the Opotiki College grounds, the bank cards and a key ring were discovered in a letter box next to the college.

Churchward told police she had thrown the wallet away hoping some teenagers would pick it up and touch it. A radio-CD player was handed to police by Churchward's mother.

Police intercepted phone calls between the 15-year-old girl, who has name suppression, and her boyfriend. These indicated he had disposed of clothing the pair had worn at the time of Mr Rowe's attack. The pair were arrested and charged 3-1/2 weeks after Mr Rowe's death.

The attack had been savage and calculated and it was the Crown's contention they had acted jointly with murderous intent, Mr McWilliam said.

Churchward's lawyer, Paul Mabey QC, told the jury Churchward did not deny striking Mr Rowe but the case was one of the distinction between murder and manslaughter and whether Churchward had acted with murderous intent.

"That is denied," he said.

The Crown has indicated evidence will be heard from 26 witnesses during the trial which is being held before Justice Geoffrey Venning.