Columbia, S.C. ? A 12-year-old boy’s confession to police that he killed his grandparents and set their house on fire was influenced by his age and an antidepressant, an attorney told the South Carolina Supreme Court on Thursday.

Christopher Pittman, now 17, didn’t understand the severity of his confession five years ago, attorney Andy Vickery argued in an appeal for a new trial.

Pittman is serving 30 years in prison after being convicted last year of killing his grandparents in their Chester County home in 2001.

Defense attorneys have argued Pittman was involuntarily intoxicated by the antidepressant Zoloft and did not know right from wrong.