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CASTLE ROCK, Colo. (KDVR) — The STEM School Highlands Ranch shooter facing trial made thousands of phone calls from jail and did drugs on the day of the 2019 shooting, witnesses testified Monday.

Jurors also heard how Erickson might have tried to warn a good friend of his to leave the classroom before he opened fire.

On the morning before the deadly shooting, Devon Erickson — who’s on trial in the murder that day of fellow student Kendrick Castillo — had snorted lines of cocaine and smoked marijuana, a friend said.

David Sispera was with his former classmate.

“We went straight to the basement, really. At first, we smoked a little bit of weed, and then me and him did a line of cocaine,” Sispera said, testifying that the two of them had talked about doing that the night before.

Before the shooting that morning, another student said Erickson appeared to have tried to lure him away from the class where the shooting was about to go down.

“He was asking me to go to the bathroom to talk about something that his dad had told him that day that he wanted to talk about,” Erickson’s classmate and friend Aaron Padgett testified, adding that he didn’t go along because he was watching a movie and taking notes.

The jury was told Erickson has made thousands of phone calls since he’s been in jail. Recordings of some those calls were played in court.

He could be heard talking to females, referencing school shootings in the conversation.

Erickson kept his head down while the recordings were played.

Jurors were also shown a gas can that may have been used to set a car on fire, as well as the guitar case used to carry weapons into the school.

A rifle and handgun were also brought out as a forensic expert with the Federal Bureau of Investigation talked about DNA samples and fingerprints found on them.

Late in the afternoon, a Sky Ridge Medical Center emergency room doctor talked about students’ wounds he treated that day.

The other student involved in the shooting, Alec McKinney, has already pleaded guilty to charges in the shooting and has been sentenced to life in prison.

Erickson’s trial could last two-and-a-half more weeks.