Five months of “horrific abuse” inflicted upon a minor.

Those are the blunt words King County Senior Deputy Prosecutor Mary Barbosa told a court two years ago to describe what 42-year-old Matthew Christenson of Auburn did to the 18-year-old, severely autistic son of the woman with whom he lived with for eight months in 2014.

Indeed, the official account of what happened in the Brookside Village apartment in Auburn paints a picture of wanton acts of malignant cruelty, including all-night ice baths, forced, pointless marches up and down the apartment building’s stairwell that lasted for hours and forcing Otto Smith to live and sleep in the bathroom.

Superior Court Judge Chad Allred sentenced the now 45-year-old Christenson on Friday morning to an exceptional sentence of 65 years in prison for his actions.

On Aug. 10, a jury at the Maleng Regional Justice Center convicted Christenson of homicide-by-abuse, three counts of second-degree assault and one count each of felony harassment and unlawful imprisonment and found him guilty of assault for beating his victim’s younger brother, the crime with which he had originally been charged.

The charges included aggravators based on an ongoing pattern of abuse, victim vulnerability and deliberate cruelty. The boys were subjected to protracted abuse, which included forced exercise, hours-long ice baths and beatings.

The sentence range was 30 to 41 years. With the aggravators, prosecutors recommended an exceptional sentence of 65 years in prison.

Senior Deputy Prosecutors Jessica Berliner and Ben Santos handled the case.

Here is what happened.

According to court records, the woman, a former special education teacher in Renton who was struggling to care for her autistic son in December of 2013 had placed an ad on Craig’s List seeking male companionship.

Unfortunately, she met Christenson.

“In no time, Christenson moved himself into her life and into her home,” court records say, and “she reported that he quickly took over her life and controlled her behavior.”

According to court records, Christenson did not want the woman on medication and told her to stop taking an anti-depressant. According to court records, the woman and Christenson drank heavily and smoked marijuana, and Christenson told her that “her kids were evil and put evil spirits in their apartment.”

According to court records, investigators found the woman “seemingly unable or unwilling to stop the abuse or protect her child,” including the alleged ice baths.

Asked to explain the ice baths, the woman speculated that “it was to reduce the swelling and bruising from the beatings Christenson inflicted,” according to court records.

On the night Smith was killed, Christenson had forced the boy to take an ice bath, as he had often done to both boys. He bound Smith hand and foot, stuck a sock in his mouth, wrapped his head in duct tape, and watched as the youth suffocated on the living room floor.

According to court records, during the early morning hours of Sunday, April 13, 2014, the boys’ mother called 911 to report that her 18-year-old son was not breathing. She later called back and cancelled the call, telling the dispatcher that “they were going to transport Otto to the hospital themselves.”

According to court records, the boy was taken to St. Francis Hospital in Federal Way, where he was pronounced dead in the emergency room. According to court records, the woman told doctors and later the King County Medical Examiner’s Office that her son had accidentally fallen down the stairs

The events came to light on Dec. 22, 2014 when King County Sheriff Deputies met with the boy’s mother at Tacoma General Hospital, where she had gone en route to Eastern Washington to escape the abusive relationship.

At first the woman told officers she’d been kidnapped, but that story soon fell apart.

During a later conversation with a social worker, according to court records, the woman claimed her boyfriend had killed her son, and that she had helped clean up the evidence.

The woman ultimately pleaded guilty to first-and-second-degree charges of rendering criminal assistance for her role in covering up the abuse and homicide.