An Alabama teenager convicted of killing five family members, including three younger siblings, when he was 14 years old has been sentenced to spend the rest of his life in prison without the possibility of parole.

Circuit Judge Chadwick Wise handed down the sentence Thursday to Mason Sisk, now 18. Wise wrote that the crime was “ghastly, disturbing, and draped in unmitigated evil” and warranted the harshest punishment allowed by law.

A jury in April convicted Sisk of multiple counts of capital murder for the 2019 shooting deaths of his father, adoptive mother and younger siblings. All five were shot in the head at their home in Elkmont. The youngest was an infant.

John Wayne Sisk, 38, and Mary Sisk, 35, were found dead in their home on Sept. 2, 2019, along with their three children – 6-year-old Kane, 4-year-old Aurora and 6-month-old Colson. All had been shot in the head.

Authorities said Mason Sisk initially told police he was in the basement playing video games when he heard gunshots and ran outside to see a vehicle pulling away, but he later told investigators he’d killed the five.

The U.S. Supreme Court said life sentences for those under the age of 18 at the time of their crimes are inappropriate except for the rarest of cases and judges should consider “children’s diminished culpability, and heightened capacity for change.”

Wise wrote that the slayings were the rare case where a life sentence without parole was warranted for a juvenile defendant. He noted the victims had been killed as they were lying in bed. He wrote that the “circumstances of the Sisk case are much more appalling” than other cases where life sentences have been upheld for juvenile defendants.

Sisk did not make a statement before his sentencing and showed no reaction when the sentence was read, CBS affiliate WHNT reported.

“I’ve prosecuted a lot of people in my career, and I can tell you that out of all of those people, only four out of five people scare the hell out of me and he’s at the top of my list,” Limestone County District Attorney Brian C.T. Jones said in a statement, according to WHNT.