The U.S. Supreme Court rejected on Monday the appeal of a youth who killed his grandparents when he was 12 years old, considering the 30-year prison sentence was suitable in his case.

Lawyers for Christopher Pittman, now 18 years old and 6 foot tall, claimed the punishment was cruel and unusual for a boy of that age, especially as Christopher was on antidepressants at that time.

Three years ago, Pittman was convicted for killing his grandparents with a shotgun in their sleep, then setting the house on fire.

“On the day of the tragic murders, 12-year-old Christopher Pittman was -- in mind, body and temperament -- a young child,” his lawyers argued, according to Bloomberg.

The lawyers also claimed that the antidepressant Zoloft, which Pittman was taking, affected the boy’s mind.

Pfizer, the maker of Zoloft did not comment on the current appeal made by Pittman, but said, according to CNN, that the drug “didn't cause his [Pittman's] problems, nor did the medication drive him to commit murder. On these two points, both Pfizer and the jury agree.”

In 2004, the Food and Drug Administration ordered Zoloft to warn doctors and patients about the drug’s risk of causing suicidal behavior in children.

There is one more factor, Pittman’s lawyers argue, that is to be taken into consideration when judging the boy’s action. Apparently, the boy had had a sad and instable childhood, changing homes and being abandoned by his mother twice. Joe Pittman, Christopher’s father, has taken care of the boy for most of his life, but their relationship deteriorated. After the boy threatened several times to harm himself, he was diagnosed as depressed and given Paxil, a mild antidepressant which is no longer recommended for children under 18.

In the night of the crime, November 28, 2001, Christopher had been beaten with a belt by his grandfather as punishment for getting involved in a fight at school, earlier that day.

Later that night, the boy took a shotgun and shot his grandparents, before setting the house on fire and fleeing in their gun.

After Pittman admitted all of these actions, he received the shortest possible sentence for murder, 30 years without parole.

Pittman’s lawyers say the boy is the only inmate serving such a harsh sentence for a crime committed at such a young age. The judge who sentenced Pittman was forbidden by law to take the boy’s age into account.

As the Supreme Court  rejected the young killer’s appeal, he will get out of jail when he is 42.