Police arrested Aaron Ybarra, 26, in the Thursday shooting at Seattle Pacific University in which two others were wounded.
A Seattle television station, citing unidentified police officials, reported that Ybarra was obsessed with the 1999 mass shooting that killed 15 people at Columbine High School.
Police declined to comment on that report and have offered no motive for the shooting at the Methodist liberal arts college of 4,000 students in Seattle's upscale Queen Anne neighborhood.
Ybarra was scheduled to make his first court appearance on Friday afternoon.
Ybarra, who was not a student at the university, is accused of walking into an academic building on campus, Otto Miller Hall, and gunning down three people before pausing to reload his weapon.
At that point, police said, a student building monitor pepper-sprayed and tackled the shooter to the ground as several other bystanders jumped in to help restrain him and seized his shotgun. He was arrested minutes later by police, who said the suspect also was carrying a knife and additional ammunition.
A man died shortly after the attack at Harborview Medical Center, while a woman was in critical condition on Friday after five hours of emergency surgery. Both were in their 20s. The third victim, a 24-year-old man, was hospitalized in satisfactory condition with pellet wounds.
A third man was treated for minor injuries suffered in the scuffle with the suspect and released, police said.
The bloodshed in Seattle marked the latest in a series of mass shootings at schools and other public places around the country in recent years that have renewed a national debate over gun safety and mental illness.
Two weeks ago, a 22-year-old man stabbed three people to death and fatally shot three others before taking his own life in a rampage across a college town near the University of California at Santa Barbara.
Ybarra, who was booked into the King County Jail, was characterized as a troubled but mild-mannered individual by an acquaintance who described himself to Seattle television station KIRO-TV as a onetime drinking buddy of the suspect.
"I didn't think he was capable of something like that," Jason Wells told KIRO. "He seemed a little bit on the crazy side but he needed somebody to reel him back."
Citing unidentified police sources, KIRO said Ybarra was preoccupied with school shootings and had visited Columbine, the Colorado high school where two students killed a teacher and 12 fellow classmates before taking their own lives in 1999.