Authorities have identified the suspected gunman as Aaron R. Ybarra, 26. Ybarra is being held without bail in King County Jail on homicide charges, according to jail records.
At an earlier news conference, Assistant Police Chief Paul McDonagh said the man in custody was not a student at the school.
A lone gunman armed with a shotgun and knife opened fire in a building at a small Seattle university, fatally wounding one person before a student subdued him with pepper spray as he tried to reload, police said.
A student building monitor at Seattle Pacific University disarmed the gunman after he entered the foyer at Otto Miller Hall, and several other students jumped on top of him and pinned him down until police officers arrived, police said.
A 19-year-old man died at Harborview Medical Center. Three other people were hospitalized. A critically injured 20-year-old woman was taken to surgery, hospital spokeswoman Susan Gregg said. A 24-year-old man and a 22-year-old man were in satisfactory condition. Gregg says one of those two men was not shot.
None of the victims in the Thursday shooting was immediately identified.
At a news conference Thursday night, Assistant Police Chief Paul McDonagh said the suspect in custody was a white male "approximately 26 years of age" who was not a student at the school. McDonagh said his name would not be released until he's booked into jail for investigation of murder.
The afternoon shooting came a week before the end of the school year, and the situation was particularly tense when police initially reported that they were searching for a second suspect. They later said no one else was involved.
The university locked down its campus for several hours, and it alerted students and staff to stay inside. Some students were taking finals in the same building that the shooter entered.
"We're a community that relies on Jesus Christ for strength, and we'll need that at this point in time," said Daniel Martin, president of Seattle Pacific University.
On Thursday evening, people packed the First Free Methodist Church on campus for a service of prayers and song. So many people crowded into the building that dozens of people gathered on a lawn near the church and formed their own groups as the sun set.
About 4,270 undergraduate and graduate students attend the private Christian university. Its 40-acre campus is in a leafy residential neighbourhood about 10 minutes from downtown Seattle. The school cancelled classes and other activities Friday.
Jillian Smith was taking a math test on the second floor of Otto Miller Hall when a lockdown was ordered.
She heard police yelling and banging on doors in the hallway. The professor locked the classroom door, and the 20 or so students sat on the ground, lining up at the front of the classroom.
"We were pretty much freaking out," said Smith, 20, a second-year student. "People were texting family and friends, making sure everyone was OK."
About 45 minutes later, police came and escorted them out of the building two by two, she said. On the way, they passed the lobby where she saw bullet casings and what appeared to be blood in the lobby carpet and splatter on the wall.
"Seeing blood made it real," Smith said. "I didn't think something like this would happen at our school."
Ashley Springer, 26, was in a classroom with her professor and a few other students when a woman with a bullhorn came into the room and told them to lock the door, pull down the shades and turn out the lights.
Springer, a senior, called Seattle Pacific University "a really close community."
The gun violence follows a spate of recent shootings on or near college campuses.
Last month, according to police, Elliot Rodger killed six people and injured seven before turning his gun on himself in a rampage in Isla Vista, California, near two universities.
Seven people were killed and three injured when a 43-year-old former student opened fire at a tiny Christian school, Oikos University, in Oakland, California, in 2012. A gunman killed five people and injured 18 when he opened fire in a Northern Illinois University lecture hall in 2008.
In 2007, 32 people were fatally shot in a dorm and classroom at Virginia Tech in Blacksburg, Virginia, before the gunman killed himself.
Seattle Mayor Ed Murray, noting previous mass shootings in the city, said: "Once again the epidemic of gun violence has come to Seattle."