A teenager who claimed he killed a classmate after rejecting his sexual advances has been convicted of murder.

Craig Roy stabbed 16-year-old Jack Frew 20 times and slit his throat.

The killer claimed that, after previously having a sexual liaison with his victim, the 16-year-old had tried to blackmail him by threatening to tell his lover that he had been unfaithful.

Roy (19) told the High Court in Glasgow he admitted carrying out the attack but claimed he could not remember it.

He said that, on May 6, 2010, he had taken a knife with him to "scare" his classmate when the pair headed into woods at East Kilbride, South Lanarkshire.

He claimed that Jack Frew exposed himself and he recalled pulling out the knife. The next thing he could remember, he said, was Jack Frew lying seriously injured on the ground.

In evidence, the court heard that Roy told a psychiatrist he "felt like a monster".

Roy was in the same class as his victim at Duncanrig High School in East Kilbride.

His defence team had pleaded guilty to culpable homicide due to diminished responsibility, claiming he suffered from a personality disorder, but this was rejected by the jury.

In a statement, Jack Frew's family welcomed the verdict.

"The verdict could have been none other than murder because that's what it was. Cold, calculating and planned murder.

"Not only has Jack had his life snatched from him but his good name has been tarnished by wicked words and lies which were unfounded.

"The family can only take comfort from the fact that those who knew Jack know and remember what he really was like.

Area Procurator Fiscal for Lanarkshire Janet Cameron said: "Craig Roy armed himself with a knife and carried out a violent, sustained and murderous attack on Jack Frew.

"Jack Frew died because Craig Roy had a knife and had no hesitation in using it and using it repeatedly.

"This crime yet again demonstrates the devastating consequences that can follow from carrying a knife.

"The senseless loss of such a young life is tragic and caused shock and concern not just to the local community in East Kilbride but across our country."