A wealthy jeweller's son has been found guilty of murdering his 17-year-old girlfriend in a jealous rage.

Elliot Turner, 20, part of a gang of rich young men who called themselves The Firm, strangled 17-year-old Emily Longley in his bed after becoming suspicious that she was seeing other men.

Turner's parents Leigh, 54, and Anita, 51, tried cover up the crime by destroying a confession note from their son after the killing at their home in Bournemouth, Dorset, in May last year. They were convicted of perverting the course of justice.

Turner was convicted following nine hours of deliberations by a jury at Winchester crown court. Nicknamed All-Talk Turner because of his boasting, he met Emily in December 2010. The pair were well known in the bars and clubs of Bournemouth and Poole.

But Turner, who had a history of obsession with women, soon showed signs of jealousy and the short volatile relationship descended into violent arguments. The court was told he threatened to kill his girlfriend almost every day.

He was described by the prosecution as "threatening, aggressive, violent, controlling and possessive towards" Emily. She went home to Auckland, New Zealand, to see her parents in April last year and Turner was incensed by Facebook pictures of her with ex-boyfriends and other men.

When Emily returned, she wanted to leave Turner and, after an argument triggered by his obsession, she slept with his best friend.

In the days before her death, Turner accessed her phone and Facebook accounts and found out she was arranging to meet men. He went to one club in Bournemouth, armed with a lump hammer, when he learned she was out with another man.

He did not find Emily but told friends he had killed her with a hammer and dumped her body in bushes before admitting it was a joke.

On the night of 6 May, Turner was furious when he met Emily and saw she was dressed in very short shorts, a leopard print bra and small waistcoat. He told her she was dressed like a whore. They argued and she threw a drink over him.

The prosecution claimed Turner used a pillow to smother Emily, then strangled her at his home in the affluent Queen's Park area. When arrested at the scene, he had his passport in his pocket and his bags packed, the court heard.

The jury was told that Turner's parents used bleach to destroy a note in which their son confessed to the killing. But police bugged the Turner house and heard the defendant say: "I just flipped. I went absolutely nuts ... I just lost it. I grabbed her as hard as I could. I pushed her like that."

In the witness box, Turner claimed Emily had attacked him and he had defended himself. He said he had loved her and she had loved him and had only wanted the best for her and he denied murdering her.

Turner will be told the minimum prison term he will serve on Tuesday.