Hundreds of students, staff and faculty attended the service at First Free Methodist Church, which was described as a time for prayer, lament and worship.
Seattle Police say 26-year-old Aaron Ybarra opened fire, killing one student and wounding two others before a student security guard, armed with pepper spray, tackled him.
Officers say once Ybarra was on the ground, other students jumped in to subdue him until police took him into custody.
The suspect was not a student at the school and police say they believe he acted alone.
Investigators haven’t released a motive in the shooting.