23-year-old Joshua Castro was arrested on Thursday.
The campus was put on lockdown after someone reported that a man with a gun a few blocks from campus.
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When officers arrived, they spotted the suspect who then took off toward the campus.
For hours, officers searched the Spartan Complex floor-by-floor, room-by-room.
They eventually found the suspect in the third-floor ceiling, hiding in the ductwork.
A handgun was found in the area.