One of the students accused of opening fire at a Denver area STEM school, killing one student and wounding eight other people, bullied younger kids and would make jokes about shooting up the school, students said.

The suspected shooter, Devon Erickson, "would whisper, like get really close and kinda put his arm around you, and whisper in your ear, ‘don’t come to school tomorrow,'" said Kevin Cole, a former student of STEM School Highlands Ranch, during an interview on "Today."

Erickson, 18, and a juvenile, who police identify as a girl but who prefers male pronouns, are accused of entering the K-12 school with handguns Tuesday. NBC News is not identifying the juvenile suspect.

Kendrick Castillo, 18, was fatally shot, and eight others were hospitalized. Several of the shooting victims have been released, and one was upgraded from serious to fair condition on Friday.

Devon Michael Erickson appears at the Douglas County Courthouse for his advisement hearing on May 8, 2019 in Castle Rock, Colorado. Joe Amon / Pool via Getty Images

One student told "Today" that the scene — which unfolded three days before Highlands Ranch seniors' last day of school — was chaotic.

"We heard yelling, we heard police tackling, screaming, singing — shockingly singing. And it was heart-wrenching," the student said. "I can still hear them faintly. I can still hear them screaming and singing."

Documents obtained by NBC affiliate KUSA show that a parent warned school officials of "a repeat of Columbine" months before shots were fired Tuesday afternoon.

In December 2018, a school district director sent a letter to Highlands Ranch executive director Penny Eucker saying a district official had received an anonymous call from a Highlands Ranch parent expressing concerns about the school and accusing administrators of a wide range of misconduct.

The parent said the school suffered from "an extremely high drug culture," "student violence due to a high pressure environment," the letter said. The parent also reported bullying, "safety issues," instances of sexual assault, and a recent bomb threat.

"The individual called it 'the perfect storm' - 'group think' and students ... are susceptible to 'copy-catting,'" the letter said. "The individual expressed concerns about a repeat of Columbine or Arapahoe."

Twelve students and a teacher were killed in the Columbine High School shooting on April 20, 1999, before the two gunmen killed themselves, and one student died after the shooting at Arapahoe High School on Dec. 13, 2013. That shooter also turned the gun on himself.

The parent said school officials had ignored her concerns. She also alleged that students had learned to build a bomb in school, students had smeared feces on the walls and were forced to clean it up with no gloves, and accused a teacher of hitting a student. The parent also asked for a financial audit at the school alleging that "money is being sent to China and Mexico," the letter said.

"The concerns expressed by this individual are very serious and need to be looked into to the extent possible" the letter to Eucker from the district said, adding a request that they be "apprised of your investigation and conclusions."

Officials guide students off a bus and into a recreation center where they were reunited with their parents after a shooting at a suburban Denver middle school, on May 7, 2019, in Highlands Ranch, Colorado. David Zalubowski / AP

Highlands Ranch parents were notified in February of some accusations made during the call, a letter from Eucker and a member of the school board showed.

"These outrageous accusations of criminal behavior of our outstanding and dedicated volunteer board threatens their very professions. An investigation by STEM Board and staff leadership revealed no evidence of these allegations,” the letter said.

The school filed a lawsuit, denying all of the allegations and accusing the parent caller of slander and invasion of privacy. The lawsuit sought to issue a subpoena for phone records that would reveal the identity of the caller.

STEM School Highlands Ranch officials, district officials and Eucker did not immediately respond to requests for comment on the letters and lawsuit in the wake of Tuesday's shooting.