The young Massachusetts Air National Guardsman who leaked dozens of classified military documents online, was called “the active shooter kid” by his colleagues — and made some worry that he could “shoot up” his workplace at Otis Air National Guard Base on Cape Cod, according to newly released documents.

An Air Force Inspector General report, completed in August, found one airman tried to warn superiors in 2022 Jack Teixeira, then 20, “exhibited a fringe thinking perspective” like that of Unabomber Ted Kaczynski, the Washington Post reported.

It was widely known on the base that the baby-faced Teixeira had been suspended in high school for threatening to “shoot up the school,” investigators found, leading some fellow airmen to refer to him as “the active shooter kid.”

He frequently talked about “living off the grid” so he could “blow stuff up,” a close colleague told superiors.

“From all our training, this was a red flag, it was tripping all the indicators,” one guardsman, whose name was redacted from the report, told Pentagon investigators.

But supervisors brushed off their worries, which dated back to the summer of 2021.

Teixeira was indicted in June on six counts of willful retention and transmission of national military information after illegally sharing dozens of classified documents on Discord over more than a year.

Teixeira, now 22, pleaded not guilty to the charges, and 15 members of the 102nd Intelligence Wing, including his former unit commander, were disciplined for failing to supervise him and neglecting to inform authorities about his espionage-like behavior.