Broughton grabbed her around the waist, but she struggled and grabbed his wrists.
When she turned her back to Broughton, he struck her with a rock, causing her to fall to the ground.
He repeatedly beat her with the rock, stopping only to pick up her handbag. The girl, who had 10 head wounds that required more than 30 stitches, staggered to a nearby house.
Broughton then went to Herewini's house, where the guard helped to stash the girl's stolen pink handbag.
Herewini was working the night Ms Aim was murdered and helped to cordon off the scene. He was charged with being an accessory after the fact and sentenced to five months' community detention and six months' supervision.
The case, in Rotorua in November, was not covered by the media because details of his part in the crime were suppressed for fear they would prejudice Broughton's trial. Suppression orders were lifted yesterday following the young killer's guilty plea.
Herewini testified against Broughton during a depositions hearing in September.
A summary of facts, released in the High Court at Auckland yesterday, said that, on the night of the first attack, Broughton and a highly intoxicated friend left a party and went to Herewini's house nearby.
Herewini left to do his security rounds but returned after about an hour and discovered Broughton had left his house. The teenager arrived back a few minutes later with blood on his T-shirt, hands and under an armpit. He told Herewini he had been in a fight at a party and might have broken the "other guy's" nose.
Herewini took Broughton to wash his hands under an outside tap and cleaned the T-shirt in the washing machine, giving him another one to wear.
The pair went through the victim's handbag, which Broughton later told Herewini he had found on a footpath. Herewini took $20 from the girl's wallet and gave the remaining $20 to Broughton before hiding the handbag in bush at the back of his property.
He then took the boy home. Police were in his driveway when he returned after they had used a dog to trace the scent from the scene of the attack on the 17-year-old.
Three days later Herewini disposed of the handbag near a sewerage plant. He later took police to the location.
Broughton denied hurting the girl when Herewini asked him about it.
On the night of Ms Aim's murder, Herewini was notified of an alarm going off at Taupo Nui-A-Tia College.
He called police after finding smashed windows at the school. An officer found Ms Aim unconscious nearby.
Herewini told the Taupo Youth Court last year that Broughton had said a Mongrel Mob prospect called Bryan had killed her and that Bryan had also borrowed his bike.
The day after this discussion, Broughton showed Herewini the baseball bat used to kill Ms Aim.
"He went and got it from under the house. It looked like it had blood on it."
A cousin of Broughton told the court the boy and Herewini were close. "He gets on almost too good with Leigh. They drink together."
