DENVER >> One of the suspects in a fatal attack at a suburban Denver high school in 2019 had become such a chronic drug user in the months before the shooting that he likely “couldn’t think, concentrate or understand” events around him that day, a toxicologist called by the defense testified Friday.

Toxicologist Wanda Guidry said Devon Erickson was severely malnourished because he ingested cocaine, marijuana and cough syrup nearly daily, and he suffered from long-term sleep deprivation and insomnia, The Denver Post reported.

“I believe it created psychiatric symptoms … disruption in mood, behavior and thinking,” Guidry said of the drugs found in Erickson’s system hours after the shooting. “He had a very difficult time figuring out or thinking of what he needed to do, what was right or what he wanted to do.”

Defense attorneys rested their case Friday without testimony from Erickson. Closing arguments are scheduled to begin Monday, followed by jury deliberations.

Erickson, 20, pleaded not guilty to first-degree murder and other charges in the May 7, 2019, shooting at STEM School Highlands Ranch that killed 18-year-old Kendrick Castillo and injured eight others. The other student charged in the shooting, 18-year-old Alec McKinney, pleaded guilty in February 2020 and is eligible for parole because he was a juvenile at the time of the attack.

Erickson was 18 at the time and could face life in prison without parole if he is convicted.

Chief Deputy District Attorney George Brauchler argued that Erickson agreed to participate in the attack as long as it looked like he was pressured into it and or could emerge as a hero by killing McKinney.

Brauchler said the students’ concocted “victim-hero” strategy unraveled after Castillo rushed Erickson when he pulled out a gun inside a darkened classroom as students watched a movie. Erickson’s gun went off, Castillo was killed and others tackled him, he said.

Their other possible scenario, in which McKinney killed himself, was stymied after an armed security guard apprehended him, Brauchler said.

Erickson’s lawyer, Julia Stancil, said her client was manipulated into joining the attack by McKinney, a new friend who preyed on him during a family crisis.