HIGHLANDS RANCH, Colo. —

A Douglas County School District letter describes a list of serious concerns from a parent who feared there may be "a repeat of Columbine" at STEM School Highlands Ranch months before Tuesday’s fatal shooting. 

Two shooters walked into the school at South Ridgeline Boulevard and Plaza Drive at around 1:50 p.m. Tuesday and opened fire on their classmates in “two separate locations," according to the Douglas County Sheriff's Office. The shooting left one student, 18-year-old Kendrick Castillo, dead and eight others injured.

RELATED: STEM School Highlands Ranch shooting: 9NEWS coverage of the tragedy

Daniel Winsor, director of choice planning at Douglas County School District, wrote the letter on Dec. 19, 2018. It was sent to STEM School Executive Director Penelope Eucker. 

In the letter, which was obtained by 9Wants to Know, Winsor outlines an anonymous call from a parent made to Douglas County School Board of Education Director Wendy Vogel. 

RELATED: Investigators look into report STEM school security officer fired at sheriff's deputy

According to the letter, the parent told Vogel the school has issues with bullying, drug use and violence.  

“Many students are suicidal and violent in school,” the letter says, citing the parent’s phone call. 

The letter also outlines concerns about the “high pressure” environment at the school. It says the parent called it “the perfect-storm” and “expressed concerns about a repeat of Columbine or Arapahoe.”

RELATED: Student killed at STEM School Highlands Ranch lunged at gunman, classmate says

RELATED: 'He wanted to be a hero’: Parents of STEM School victim Kendrick Castillo mourn loss of son

The April 20, 1999, attack on Columbine High left 12 students and a teacher dead and more than 20 others injured. The shooting at Arapahoe High on Dec. 13, 2013, left one student and the gunman dead.

The letter asks “STEM investigate the allegations” to determine “their legitimacy, and to take any remedial action that may be appropriate.” 

Eucker said in a statement sent Thursday to 9NEWS that STEM School immediately opened an investigation into the complaints, most of which are similar to those many schools receive — and some that were more unusual, such as staff or board members embezzling money and laundering it in China and Mexico, forcing students to clean up human feces with their bare hands and teachers instructing students how to build bombs in class.

"While STEM took the allegations seriously, our investigation revealed no evidence to support any of the allegations raised in the anonymous complaint," the statement says.

STEM's administration team reached out to its 2,800 parents to inform them of the complaint in hopes that students or family members with knowledge of the allegations would share information, according to the statement.

"STEM did not receive responses from any parents or students with information about these allegations," the statement says.

In the letter from Winsor, the district also informed STEM School that it relayed the parent’s concerns to the Colorado Department of Human Services and to the Douglas County Sheriff’s Office. 

In response to the letter, 9Wants to Know learned Eucker also filed a civil lawsuit against the anonymous caller, listed as “Jane Doe,” for making “defamatory statements.” 

The lawsuit was filed in January and is still pending. 

“Jane Doe engaged in extreme and outrageous conduct by, among other things, waging a campaign to publish wildly false and outrageously defamatory statements with the obvious purpose of destroying Dr. Eucker’s reputation,” the suit says. 

RELATED: 'Don't let fear rule you': Student who charged shooter at STEM School praises fallen classmate

RELATED: 1 student killed, 8 others injured when classmates open fire at STEM School Highlands Ranch

In February, Eucker and STEM Board President Mark Alpert sent a letter to parents denying the allegations made by the anonymous caller. 

“An anonymous call was made to a Douglas County School District board member in mid-December accusing our school leadership and Board of serious criminal behavior. 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 joint letter said. 

RELATED: The history of STEM School Highlands Ranch

9Wants to Know is waiting to hear from the Douglas County School District for comment. 

> Click/tap here to view the full letter from Winsor, the district official.

> Click/tap here to view Euker's full statement to 9NEWS.

If you have any information about this or any story, email blowthewhistle@9news.com

SUGGESTED VIDEOS | STEM School Highlands Ranch Shooting