DOUGLAS COUNTY, Colo. (CBS4) – One of the two teens charged in a Highlands Ranch school shooting that killed one student and injured eight others has pleaded not guilty. Devon Erickson, 18, entered his plea in court on Thursday.

(credit: CBS)

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Erickson’s attorney notified the court they may use a mental condition in his defense. Erickson and Alec McKinney, 16, face murder and attempted murder counts in the May 7 shooting at STEM School Highlands Ranch.

The 18th Judicial District Attorney, George Brauchler, hopes those mental exams won’t delay the case.

“This crime occurred 240 days ago. This isn’t something- an issue- that was brought up for the first time at the beginning of December and I made my argument, a record in court, about ‘look, it’s time to move forward with getting this case set,” said Brauchler.

Devon Erickson makes a court appearance at the Douglas County Courthouse on May 15, 2019. (credit: Joe Amon-Pool/Getty Images)

Police say the teens walked into the school and opened fire with handguns in two classrooms.

Maria and John Castillo, parents of Kendrick Castillo, seen leaving a courtroom. (credit: CBS)

Student Kendrick Castillo, 18, was killed when he and two classmates tackled one of the shooters. The other was captured by an armed security guard.

Kendrick Castillo (credit: Charles Burroughs)

Kendrick’s father, John Castillo, believes the mental health issue is not valid.

“I guess I’d rather see it on the front end and we can debunk it and move forward with the crime that was committed,” said John Castillo. “Diminished mental capacity was not something that took place here, it was a well-orchestrated crime with a plot to cover what they did.”

The lead detective in the case for the Douglas County Sheriff’s Office, Brian Pereira, interviewed Erickson twice following the shooting. He said the teen told him his goal was to “save as many lives as possible.” But under questioning by the prosecution the detective indicated there was no evidence of any such attempt to save people.

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Devon Erickson

Devon Erickson (credit: CBS)

Pereira said that Erickson told him he fired only one shot by accident striking the one person who died — Kendrick Castillo. But the detective indicated there were multiple shots fired from Erickson’s gun.

(credit: CBS)

It was previously revealed that Erickson had “God” written on his chest at the time of his arrest. The words “the voices win” were found written in red ink in his parents’ closet where the guns were taken for the shooting.

Devon Erickson

Devon Erickson (credit: CBS)

Pereira also told the court “F-Society,” 666 and a pentagram were spray painted on a car in Erickson’s family garage. That car was set on fire before the pair left the house for the school.

Alec McKinney (credit: Instagram)

The detective previously said Erickson told him that his co-defendant Alec had someone in particular at the school to confront.

Devon Erickson

Devon Erickson (credit: CBS)

Both suspects have been charged as adults. McKinney’s attorney wants his case moved to juvenile court.

Erickson is scheduled for trial on May 25.

(Photo by Michael Ciaglo/Getty Images)

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STORY NOTE: McKinney was born a female who identifies as male and the judge ruled that he should be referred to Alec.