PORTLAND, Ore. — An Oregon teenager who carved a swastika into another teen’s forehead as he and others tortured the boy has been sentenced to 11 years in prison.

In a Portland courtroom Thursday, 16-year-old Blue Kalmbach told the victim in a barely audible voice that he was “very sincerely sorry.”

Kalmbach was the last of four teenagers to be sentenced in the case.

“It’s almost impossible to imagine this could happen between friends, but it did,” Multnomah County Judge Jean Kerr Maurer said when accepting Kalmbach’s guilty pleas on kidnapping, robbery and assault charges.

Police and prosecutors said the teens spent the evening before the February attack sketching out ideas for torturing the victim.

Before Kalmbach carved the swastika with a box-cutter style of knife, they shot the victim with a BB gun, forced him to eat cat feces and hit with him a crow bar and cricket-type bat.

The victim, bangs covering his forehead, sat with his mother and girlfriend in court. He did not make a statement or speak with reporters.

His mother said the scar has mostly healed, but her son, who turned 17 on Wednesday, has nightmares. She said he plans to attend an alternative high school this fall and study to become an auto mechanic.

“The biggest question I have is: How can anyone do this to another human being?” she said in court.

Later, she told reporters her son has yet to forgive Kalmbach, who once was his best friend. “(He’s) still very angry, as I am,” she said.

The Associated Press is withholding the mother’s name to avoid identifying the victim.

Public defender Casey Kovacic said the case is more complex than what has been reported. He described Kalmbach as a “deeply, deeply depressed kid” who has never fit in. A statement from Kalmbach’s parents said there’s no excuse for what happened, but their son was in and out of therapy before the attack.

It’s not entirely clear what triggered the teens to torture the victim. Kalmbach told investigators the victim had bullied him and called him a derogatory name on Facebook. The victim’s mother, however, has said the bad blood began when a girl broke up with Kalmbach and started dating her son.

The violence began when 15-year-old Jenna Montgomery invited the victim to hang out with her. After meeting up, they walked to a home and into a backyard shed, where three boys confronted him. When the torture ended, Montgomery walked the victim out to the street and left him there. The victim went to a nearby business for help.

Montgomery was sentenced last month to nearly 10 years in custody, and 17-year-old Jess Taylor was sentenced to seven years and nine months. A 14-year-old was sentenced in juvenile court to 10 years at the MacLaren Youth Correctional Facility.