Ms Evans was stabbed and beaten, the court heard
An 18-year-old woman choked to death on her own blood after being lured to a park and stabbed, a court heard.
Louise Evans was taken to Towneley Park in Burnley by two housemates after one complained she was "doing his head in", Preston Crown Court was told.
She was stabbed with such force that the knife handle snapped off and the blade was left embedded in her chest.
Matthew Maw, 19, has pleaded guilty to murder but Anthony Wood, of Elizabeth Street, Burnley, denies the charge.
The pair had lived with the victim for a short time at a hostel for the homeless in the town.
They were part of a group of youngsters who had been on a drinking session the evening before the attack on 21 July.
During the night, Wood was said to have been annoyed with the victim - who had Asperger's syndrome - because she was "loud" and "bouncing around".
Prosecutor Louise Blackwell QC said he told members of the group he was "going to kill her", but they assumed he was joking.
Miss Blackwell said: "It is the prosecution's case that he took the knife with him intending it to be used on Louise Evans."
It was Maw who attacked her first with a knife and then with a large piece of wood, Miss Blackwell added.
Matthew Maw has already admitted a murder charge
The court heard that no-one in the group saw the attack but one girl said she heard a "horrible, piercing scream" before Maw asked if there was a brick available.
The court was told Wood was heard to reply: "No, if there was I would do it myself."
The girl said she shone her mobile phone towards the scene and saw the pair "grinning". Miss Evans was on the ground with blood covering her face.
Another witness told police he heard Maw scream angrily for up to a minute, then a "crushing sound" and up to 30 large thuds, the court heard.
Police were called and paramedics arrived to find Miss Evans with multiple slash and stab wounds, with her throat lacerated and front teeth missing.
A post-mortem examination showed she suffered 39 injuries to her neck, head, chest and arms.
Post-mortem tests concluded the extensive facial fractures would have led to asphyxia and the likely cause of death was from inhaling her own blood, Miss Blackwell added.
Wood told police that he had not threatened Miss Evans at any stage and played no part in her death.
The trial was adjourned until Wednesday.