The wounded were rushed to Harborview Medical Center, where one victim, a 19-year-old man, died shortly after arrival.
A 19-year-old woman was listed in critical condition Friday morning after a five-hour surgery, a hospital spokesman said. A 24-year-old man was listed in satisfactory condition.
A 22-year-old man who sustained minor injuries in the scuffle with the suspect was treated and released. He was not shot.
The gunman walked into Otto Miller Hall just after 3 p.m. armed with a shotgun and a knife and opened fire on three people, said Capt. Chris Fowler with Seattle police. The gunman then began reloading when a student building monitor pepper-sprayed the shooter.
"The shooter began to reload his shotgun and the student building monitor inside the hall confronted the shooter and was able to subdue the individual," Fowler said. "Once on the ground, other students jumped on top of them and they were able to pin the shooter to the ground until police arrived."
Fire officials on the scene originally indicated there were seven wounded including the shooter, but have since brought that number down to four victims. The suspected gunman was also injured, but not seriously.
Student Chris Howard was inside Otto Miller Hall working on a design project when the shooting began. He said he saw a woman on the ground with an apparent gunshot wound to her chest.
"She was in shock and thought she was going to die," he said. "We had to reassure her several times, no she's going to get through this."
Witness Briana Clarke was also inside the hall when the shots rang out. She was still unsure what was happening when she saw students running down the halls.
"I first heard two muffled shots that I thought were two helium balloons," she said.
Clarke then said she saw injured students inside the building and when she went outside, she saw several more bloodied students.
'When I walked outside and saw someone down, that was disturbing seeing a bunch of bullets around, the blanks all around and red that was a very disturbing image," Clarke said. "Seeing my friend outside being treated that's was hard to swallow, that a fellow student, that it could have been you."
The university was on lockdown for about two hours after the shooting but it was lifted just after 5 p.m.
Mary Jones was on campus Thursday to help her daughter move out. While grateful that her own child wasn't hurt, she wonders what can be done to stop further shootings.
"Where are the controls to keep our children from purchasing a handgun or any other kind of weapon? And does that take government controls to keep that from happening? I don't know," she said. "There has to be a greater understanding of what that weapon can do and the pain it can inflict on another person's life."
Speaking on campus Thursday evening, Seattle Mayor Ed Murray thanked the first responders and spoke about what he called an "epidemic of gun violence" in the city.
"Today should have been a day of celebration at the end of the school year at SPU, instead it's a day of tragedy and loss," he said.
The accused gunman, identified as Aaron Ybarra, was arrested and will be booked into King County Jail for investigation of murder, according to police sources. Assistant Seattle police chief Paul Mcdonagh said the suspect is 26-years old and is not an SPU student.
Police believe the gunman acted alone, but will continue to investigate.
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 neighborhood about 10 minutes from downtown Seattle. The school canceled classes and other activities Friday.