A teenager accused of shooting students at a suburban Denver high school appeared to develop a "deep fascination" with mass shootings and shared neo-Nazi views online months before the attack, research by the Anti-Defamation League found.

Authorities said Desmond Holly, 16, died from self-inflicted injuries on Sept. 10 after he fired a handgun inside and outside Evergreen High School in Jefferson County, Colorado. The shooting, which left two students critically injured, forced the school into a brief lockdown and prompted a massive police response.

Further investigation revealed that Holly had been "radicalized by some extremist network,” according to Jacki Kelley, a spokesperson for the Jefferson County Sheriff's Office. But additional details on the suspect and his alleged radicalization were not immediately released.

In a report published Sept. 12, the Anti-Defamation League’s Center on Extremism found that Holly had been active on a so-called online "gore" forum, where users share violent and graphic images and videos, since December 2024. These forums typically feature real-life acts of violence, such as murders, executions, and animal abuse, according to the ADL.

"Research by ADL Center on Extremism indicates that Holly spent substantial amounts of time in online spaces featuring extremist ideologies and violent content, ultimately adopting extremist views himself," the report states.

The report noted that Holly was one of "several mass attackers" who had been active on the forum, including two students who appeared to have died by suicide after carrying out shootings at schools in Madison, Wisconsin, and Nashville. In another report published last month, the ADL detailed how the suspects in the shootings shared similar paths as they adopted white supremacist views from online extremist communities.

What happened in the Colorado high school shooting?

On Sept. 10 at around 12:24 p.m. local time, the Jefferson County Sheriff's Office said it received reports of a shooting at Evergreen High School, about 30 miles southwest of Denver. The suspect, who was armed with a revolver handgun, opened fire inside and outside of the school while some students were at lunch.

One of the victims was shot inside while the other was shot outside, according to the sheriff's office. Following a brief lockdown, the school — which serves about 900 students — was declared safe by law enforcement.

Responding officers did not fire any rounds and found the suspect, who was later identified as Holly, within five minutes of arriving at the scene, according to Kelley. The suspect died from self-inflicted injuries, she said, adding that he had "brought quite a bit of ammunition with him."

"He would fire and reload, fire and reload, fire and reload," Kelley said at a Sept. 11 news conference. "This went on and on. And as he did that, he tried to find new targets."

Authorities have not released a possible motive in the shooting, saying that the investigation remains ongoing. Kelley previously said investigators were searching the suspect's home, school locker, and phone.

Following the shooting, the high school canceled classes on Sept. 11 and Sept. 12, and Kelley said the school will remain closed as the investigation continues. In an update on Sept. 15, the school said students will not return to class for the week.

Evergreen High School is located about 20 miles from Columbine High School, the site of an infamous 1999 mass shooting that killed 12 students and a teacher. Columbine's shooting is considered one of the deadliest school shootings in American history.

Colorado shooting suspect displayed neo-Nazi views on social media

According to the ADL, Holly had expressed neo-Nazi views online and began to collect tactical gear in the months leading up to the Evergreen High School shooting. The report added that Holly made posts on social media displaying his gear, which were decorated with extremist symbols and inspired by equipment used by previous mass shooters.

Holly's TikTok accounts were "filled with white supremacist symbolism," the ADL said, noting that his most recent account's username included a reference to a popular white supremacist slogan. His profile photo was also an image of the suspect in the 2014 Isla Vista killings, in which a 22-year-old killed six people in a shooting rampage near the campus of the University of California, Santa Barbara.

"Holly also expressed admiration for school shooters and was active within the True Crime Community (TCC) on TikTok, whose adherents have a disturbing fascination with mass murderers and serial killers," the ADL said in the report. "Holly joins a long list of mass attackers who have engaged with TCC content online, including the 2025 Antioch and 2024 Abundant Life shooters."

A few days before the shooting on Sept. 10, the ADL said Holly posted on TikTok showing himself posing in a "similar manner" to how the suspect in the Madison, Wisconsin, shooting posed before two people were killed at Abundant Life Christian School in December 2024. He included a photo of the Wisconsin shooter in the post.

The post also showed him wearing a black T-shirt with "WRATH" written on it, which Holly had recreated to match a shirt one of the gunmen wore in the 1999 Columbine shooting, according to the ADL.

Another TikTok post shared by the ADL showed that in June of this year, Holly had liked a comment from another user who asked him about becoming a "hero," a term the report says is used by some white supremacists to refer to successful ideologically motivated attackers.

The same user told Holly to get a patch with a Nazi-era symbol that suspects wore in the 2019 Christchurch, New Zealand, mosque shootings and the 2022 Buffalo, New York, supermarket shooting, according to the ADL. Holly then responded with a photo of two patches he made with Nazi-era symbols.

"I have some I made but the Velcro fell off the back," he said in the response, according to the ADL. "I’m gonna use stronger glue when I fix it."

Experts say online 'gore' forum is a 'gateway to extremism'

The ADL said Holly's activity on the online "gore" forum is the "third example in less than a year of a teenager using the platform, becoming radicalized and committing a school shooting or murder."

Holly had an account on the forum, where he had commented on posts about previous mass shootings, such as the 2018 Parkland high school attack, the 2022 Buffalo shooting, and the 2017 Quebec City mosque shooting, according to the ADL. The report added that Holly may have joined the forum on Dec. 26, 2024, more than a week after the Abundant Life Christian School shooting.

The report noted that the forum "served as a gateway to extremism" for at least three suspects in school shootings, including Holly and the suspects in the Abundant Life Christian School shooting and Antioch High School attack in Nashville. The ADL added that it had originated on Reddit, a social media platform, before it was banned from the site in 2019.

"As ADL’s research has revealed, white supremacist, antisemitic and other extremist content is frequently posted on the site," the report states. "Young people can readily access extremist content and visual depictions of graphic violence that are celebrated by users of the platform, potentially desensitizing them to such content and increasing the risk of ideologically-motivated violence."

Contributing: Julia Gomez, Eduardo Cuevas, and Michael Loria, USA TODAY

This article originally appeared on USA TODAY: Colorado school shooting suspect had 'deep fascination' with mass shootings, ADL says

Reporting by Thao Nguyen, USA TODAY / USA TODAY

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