(CNN) -- When Briana Clarke heard popping sounds on a Seattle college campus Thursday, she thought the source must be something innocent -- bursting balloons. Then she saw a classmate running frantically, saying someone had been shot.
A gunman had opened fire at Seattle Pacific University, killing one person and wounding two more before he was tackled by a student security guard, Seattle police said.

The gunman was reloading a shotgun when the tackler, working as a building monitor, used pepper spray and knocked him down, police Capt. Chris Fowler told reporters.

"Once on the ground, other students jumped on top of them and subdued the shooter," he said.
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The suspect, 26-year-old Aaron Ybarra, is not a student at the school, police said.