DOUGLAS COUNTY, Colo. (CBS4) – During day four of Devon Erickson’s murder trial, jurors heard testimony from crime scene investigators and students inside STEM School Highlands Ranch. Prosecutors say Erickson and another student, Alec McKinney, opened fire on students and staff more than two years ago.

“You have the most dramatic moments of your life and have to make sure you are describing it in the most appropriate way,” said Tyler Strimbu, one of the students who testified.

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Tyler Strimbu (credit: CBS)

Those dramatic moments happened as Strimbu was in class in 2019. Now, he was asked to recall for a jury when he saw Erickson pull out a gun.

“I thought he is going to be in a lot of trouble. This is a late senior prank,” Strimbu told CBS4’s Rick Sallinger.

He and the others quickly found out it was no prank.

“As he pulled out the gun he said, ‘Nobody f—ing move.’ Three people charged him and then there were shots.”

He said he hid in a corner of the classroom by bookshelves until he heard someone shout “everybody run.”

(credit: CBS)

“At which point I stepped over Kendrick’s body.”

That was Kendrick Castillo, the 18 year old who was killed trying to take the gun away.

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“It’s not very often you are asked to talk about it and look back on it and remember things… Kendrick,” Strimbu told Sallinger.

Kendrick’s father, John Castillo, has been attending the trial daily with his wife.

“It’s just indescribable. I think anybody watching can imagine how we feel,” he said.

Strimbu pointed out for the jury in model where exactly it all happened. He said he saw Alec McKinney on the ground.

“You were in that classroom. Is there anything you would do differently?” Sallinger asked Strimbu.

ascent classical academy DOUGCO ARMED TEACHER

STEM School shooting in May of 2019. (credit: CBS)

After a thoughtful pause he replied, “No.”

Erickson claimed McKinney forced him to take part in the school shooting or he would be killed. Prosecutors insist it was a partnership, and McKinney did it to inflict pain on others as McKinney has felt going through school as a transgender boy.

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McKinney pleaded guilty and received a life sentence. Erickson faces 48 counts including murder.

Rick Sallinger