The gunman acted alone, and was immediately stopped by a citizen fighting back, but police, having arrived,  decided to search the (mostly white) students.

A shooting in Seattle  by Hispanic gunman was stopped by a student who fought back.

A gunman had opened fire Thursday 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.

The suspect, 26-year-old Aaron Ybarra, is not a student at the school, police said.

They say they think he acted alone, but the investigation is continuing. Police did not disclose a motive.

Three shot at Seattle Pacific University before student tackles gunman

By Ben Brumfield, Ralph Ellis and Chelsea J. Carter, CNN updated 11:53 AM EDT, Fri June 6, 2014

The student who tackled him was armed with pepper spray.

Who is the student who pounced on the Seattle gunman? A hero, many say

By Ben Brumfield, CNN updated 11:00 AM EDT, Fri June 6, 2014 (CNN) — Jon Meis' reported habit of carrying pepper spray may have saved students' lives after a man opened fire at a Seattle college.

The shooter had just wounded three people Thursday, one of whom died. He was reloading his shotgun when Meis, a volunteer security guard, saw an opening.

He doused the gunman with the spray and tackled him to the ground.

Other students at Seattle Pacific University piled on and took the weapon away from suspected shooter Aaron Ybarra, 26, police said.

Officers are convinced the bloodshed at the Christian school would have been worse had Meis and the others not intervened.[More]

I should mention that SPU is a Christian school,  founded by Methodists. That may give some clue to the motive. See if that gets in any of the headlines.

The SPU Office Of Safety And Security reports almost no crime on campus.

Typically, they also have rendered the students defenseless. This is from the SPU student handbook:

Weapons

The possession, use, storage, manufacture, transport, display, sale or distribution of firearms and other weapons is prohibited on or around University property, including student rooms and common areas. If your circumstances do not allow you to leave these items at another location, you must ask [the Office Of Safety And Security]to store them for you. Prohibited weapons include but are not limited to: BB pellet guns, paint guns, airsoft guns, stun guns, Taser devices, martial arts weapons, folding knife blades over 3 inches long, bows and arrows, slingshots, water balloon launchers, any other weapon listed in the Revised Code of Washington (RCW) 9.41, and any form of ammunition. Realistic facsimiles of weapons and counterfeit weapons are also prohibited. [PDF]

I see it doesn't specifically say "pepper spray"—perhaps that comes under "are not limited to"—and they might actually add that, now that this has happened.