EVERGREEN, Colo. — The Jefferson County Sheriff's Office said Thursday that the 16-year-old student who opened fire at Evergreen High School on Wednesday was "radicalized by some extremist network," but did not provide further details.

A report released Friday by the Anti-Defamation League's Center on Extremism, however, revealed more about the student's activity online in the months before he brought a revolver to school and fired several rounds.

Specifically, the report states the shooter was active on an online gore forum where two other school shooters had also been active before carrying out their attacks, both within the last year.

Since December, the shooter had been active on the forum where users watch videos of killings and violence, mixed in with content on white supremac

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