He was convicted in August on several counts.

Associated Press

SEATTLE — A Washington state man convicted of severely abusing and then killing the 18-year-old autistic son of his girlfriend was sentenced to 65 years in prison.

The Seattle Post-Intelligencer reported that Matthew Christenson was sentenced Friday after he was found guilty on several charges involving the 2014 abuse and death of Otto Smith.

Christenson was convicted in August for homicide by abuse, second-degree murder, three counts of second-degree assault, unlawful imprisonment and felony harassment.

Authorities said Christenson had forced Smith to take an ice bath, and then he bound Smith’s hands and feet and wrapped his head in layers duct tape, causing his death. Christenson was also convicted of abusing Smith’s 13-year-old brother.

Christenson has said that he is innocent and that he is appealing his convictions.