Police said a suspect is in custody after a campus shooting left a 20-year-old man dead and three others injured at Seattle Pacific University around 6:30 p.m. EST Thursday night.

Authorities initially reported two suspects in the attack, but now say all suspects are in custody. The source of the confusion was not immediately clear, though KIRO-7 Seattle cites a source familiar with the investigation who said the second man may have been attempting to disarm the shooter.

Police said the suspect walked into Otto Miller Hall on the campus, approached three students and started firing his weapon. A student security guard attacked the gunman with pepper spray, with other students moving in to help subdue the attacker as he stopped to reload.

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Seattle Times cites an eyewitness who said the security guard, whom she identified as student Jon Meis, sprayed the gunman, grabbed his neck and wrestled him to the ground.

A campus lockdown has been lifted, the school’s student newspaper reports, though university officials are asking students to avoid the area.

One witness described walking through a “pool of blood” as they left the building to local reporters.

About 4,000 students attend the private Christian university.

“Today should have been a day of celebration at the end of a school year,” Seattle Mayor Ed Murray told reporters at the scene. “Instead, it’s a day of tragedy and loss. Once again, the epidemic of gun violence has come to Seattle, the epidemic of gun violence that has haunted this nation.”

The Seattle Times has compiled a list of mass shooting incidents in the city since 1983.

This story is developing and will be updated with more information as it becomes available.