Authorities believe only one person fired the shots Friday night at Cascade Mall in Burlington, about an hour north of Seattle.
A search is underway for an armed man who headed toward Interstate 5 after the attack, said Sgt. Mark Francis, a spokesman for the Washington State Patrol.
Francis released a blurry surveillance photo of a man described as the suspect. His motive or relationship to the victims, if any, are unclear, he said.
The names of the victims were not immediately released.
Camera footage from FBI
Moviegoers asked to leave
Witnesses described chaotic scenes and confusion when the shooting started about 7 p.m. local time
Brandi Montreuil told CNN she was watching a movie at the mall when attendants suddenly told them to leave.
“I didn’t know anything,” she said. “The theater attendant came in and apologized for stopping the movie and said they were asked to have everyone leave immediately.”