Petric's lawyers argued he was not guilty of murder on insanity grounds
A US teenager killed his mother and wounded his father in revenge after they took away his violent computer game, a judge has ruled.
The defence team for Daniel Petric, 17, had argued his addiction to the Halo 3 game, in which players shoot invading aliens, had made him insane.
But the judge rejected this, saying he had planned revenge for weeks.
Petric, of Ohio, was tried as an adult and faces a maximum possible penalty of life in prison without parole.
On the night of the shooting in October 2007, Petric used his father's key to open a lockbox and remove a 9mm handgun and the game, the court heard.
His father Mark, who was shot in the head and survived, testified that his son came into the room and asked: "Would you guys close your eyes? I have a surprise for you."
He said he expected a pleasant surprise. Then his head went numb from the gunshot.
The Associated Press news agency reports that Microsoft, which owns the intellectual property for the game, declined to comment beyond a statement saying: "We are aware of the situation and it is a tragic case."