Elliot Turner, who is charged with murdering his New Zealand girlfriend Emily Longley, has how pleaded guilty to perverting the course of justice.

Turner, 20, denies murdering the 17-year-old aspiring model in his bedroom at the family home in Bournemouth, Dorset.

But in Winchester Crown Court on Monday he changed his plea on the other charge after it was amended to take away reference to Turner failing to call an ambulance following Emily's death.

His father Leigh Turner, 54, who along with his mother Anita have denied charges of perverting the course of justice, told the jury that paranoia led him to believe a letter he found could have been a confession that his son murdered Emily.

Leigh Turner said he did not read the letter from Elliot to his mother and he had ripped it up.

He later had learnt a little of what was in the note when he overheard his wife and son talking about a mallet, an argument and being hit.

He said there was no excuse for destroying the letter, but he denied he realised he was perverting the course of justice when he did it.

He also denied taking a jacket from the house when it was a crime scene.

The prosecution alleges Elliot Turner strangled Emily in a jealous rage on May 7 last year after he feared she was seeing other men.

Leigh Turner told the jury he had returned home after a call from his wife that Emily "might be dead".

"She looked like she was asleep for that split second," he said. "I knelt down beside, her touched her cheek, touched her head and touched the side of her neck. She was cold - ice cold, like a crystal cold. The girl had passed away.

"I said 'sorry butterfly' or something like that, I'm crying."

He said his son had packed a suitcase and he had said to him: "What are you going for? There is nothing to run from."

Leigh Turner said what he was heard saying, on tapes covertly recorded by police, about Elliot strangling Emily was the "worst-case scenario of what might have happened".