An Oregon teen pleaded guilty to killing an 18-year-old cancer survivor during a robbery at a hotel.

Jeremiah Terrel Hannon, 17, pleaded guilty Wednesday to second-degree murder in the December 2018 slaying of Ian Olson, a lymphoma survivor who was found shot in the back of his head by a worker at a Motel 6 in Portland just days before Christmas in 2018, The Oregonian reported.

Hannon, who was 15 at the time of the slaying, was sentenced in Multnomah County as a juvenile to up to 20 years of confinement, but he must be released by his 25th birthday according to state law, the newspaper reported.

Few details of the killing were released by authorities, including how the teens got to the motel and what Hannon took from Olson, but prosecutors said it occurred during a two-month crime spree by Hannon that included an attack on a MAX Light Rail train that left a man with a broken jaw.

Prosecutors also read a letter from Olson’s mother saying that her son is gone forever while Hannon will be released from a juvenile facility in a “few short years,” The Oregonian reported.

“Not one day doesn’t [go] by that I don’t cry for Ian,” the woman’s letter read. “There’s no amount of time that’s acceptable for what you’ve done.”

Olson, who survived two types of lymphoma, had been “cancer free” for a week prior to the slaying, his mother wrote.

“You took that all away from him on the night of Dec. 21, 2018,” her letter read.

A lifelong friend of Olson’s, Jordan Rhode, said the teen never complained about his disease or having to undergo intense chemotherapy.

“I was going to the hospital almost every single day,” Rhode previously told KPTV, saying he would sit next to Olson during the treatments. “I always felt like he was going to beat cancer, too. I knew it. And, that’s what happened.”

An attorney for Hannon, meanwhile, read from a statement her client made nearly a year ago apologizing for the slaying. The teen also pleaded guilty Wednesday in the December 2018 train assault and stealing another person’s phone days later, The Oregonian reported.

“I can’t take it back,” Hannon wrote in his statement shared by attorney Dawn Andrews. “I’ll try to make myself right so I don’t put someone else through nothing like this … I’m truly sorry.”