Stefan's mother, Giselle, a research nurse, had to leave court when the evidence in the case became too harrowing.

Following the hearing she said her son's killer had mimicked a game called Manhunt, developed by Edinburgh-based Rockstar North, in which the players score points for violent killings.

Mrs Pakeerah said: "I heard some of Warren's friends say that he was obsessed by this game.

"To quote from the website that promotes it, it calls it a psychological experience, not a game, and it encourages brutal killing.

"If he was obsessed by it, it could well be that the boundaries for him became quite hazy."

Mrs Pakeerah, 36, called for violent video games to be banned.

Outside court Stefan's father, Patrick, said: "They were playing a game called Manhunt.

"The way Warren committed the murder is how the game is set out - killing people using weapons like hammers and knives.

"There is some connection between the game and what he has done."