Suspect Devon Erickson, 18, often shook his head when replying to the judge, according to The Associated Press. He responded “no” when asked if he had any questions.
Erickson and a second suspect – a juvenile – are accused of the attack at the STEM School Highlands Ranch.
Charges in the case against Erickson are set to be filed on Friday afternoon local time, Rob McCallum, the public information officer for the Colorado Supreme Court, tweeted.
The Douglas County coroner identified the slain student as Kendrick Ray Castillo, the sheriff’s office announced. Castillo, 18, was killed when the suspects opened fire in a classroom at the K-12 charter school located south of Denver. The teen is reportedly credited with saving the lives of his classmates.
While in a British literature class, Castillo, "lunged [at the suspect]," and was shot because of it, according to a fellow student at the school.
Nui Giasolli told NBC News' "Today" show on Wednesday that Castillo's actions "[gave] all of us enough time to get underneath our desks, to get ourselves safe, and to run across the room to escape.”
Fox News’ Nicole Darrah, Bradford Betz and The Associated Press contributed to this report.