The gunman forced his way through the security door at the federation after an employee had punched in her security code, Marla Meislin-Dietrich, a database coordinator for the center, told The Associated Press.
"He said `I am a Muslim American, angry at Israel,' before opening fire on everyone," Meislin-Dietrich said. "He was randomly shooting at everyone."
Booked into jail late Friday night for investigation of homicide and attempted homicide was Naveed Afzal Haq.
Asked if the suspect was a Muslim, Seattle Police Chief Gil Kerlikowske told an evening news conference "you could infer that that was his background."
Haq, 30, previously lived in Pasco, one of southeast Washington's Tri-Cities, Seattle police said in a statement released late Friday night.
One woman died at the scene and five others were under treatment at Harborview Medical Center, Kerlikowske said.
When the shots rang out around 4 p.m. Friday, employees fled the center in terror as nearby police officers charged to the scene and blocked off several downtown blocks.
The gunman turned himself in to a SWAT team just minutes after the shooting began. He spoke with a 911 dispatcher, a phone call that led police to tag the shooting as a hate crime. Mayor Greg Nickels and Kerlikowske said officers were moving to protect both synagogues and mosques around the city, but said there was no evidence of a broad conspiracy.
"This was a purposeful, hateful act, as far as we know by an individual acting on his own," Nickels said.
Kerlikowske said they were protecting mosques "because there's always the concern of retaliatory crime."
Laura Laughlin, special agent in charge of the Seattle FBI office, said the arrested man was a U.S. citizen and agents were working to contact his relatives.
Authorities have been advising synagogues and Jewish groups to be watchful in the weeks since hostilities erupted between Israel and Lebanon. Assistant Police Chief Nick Metz said the warning was not in response to any specific threats.
Three of the injured women were in critical condition after being shot in the abdomen, hospital spokeswoman Pamela Steele said. Two others were in satisfactory condition: a 37-year-old woman, five months pregnant, who had been shot in the forearm; and another woman who was shot in the knee, Steele said.
Several witnesses said they saw a man walk up and shoot a woman in the leg on a sidewalk near the federation building. One witness, who refused to give his name, said that shooting was just outside a nearby Starbucks. There was a small pool of blood outside that coffee shop.
Police evacuated several nearby buildings as SWAT teams searched the federation building, looking for any other victims, anyone hiding or any other possible shooters.
Patti Simon was at work at the federation's newspaper on the first floor when she heard screaming, shots and what sounded like furniture crashing on the floor above.
"We heard this horrible screaming on the floor above us and shots," said Simon, 52, who sells advertising at the paper. Simon called up to her co-workers on the second floor, but got no answer, so she called the police and fled the building.
"People got shot, some of our co-workers," Simon said, her voice shaking. "I just got back from Israel and made it out of there a half hour before the rockets started."
The federation's Web site describes its mission as "to ensure Jewish survival and enhance the quality of Jewish life by meeting needs locally, in Israel and worldwide." It was among sponsors of a Solidarity With Israel rally last weekend.
FBI Special Agent Fred Gutts said that on July 21 and 26, the Seattle office sent general warnings to local law enforcement agencies in the state to be on heightened alert around Jewish-related buildings given the hostilities in the Middle East. He said local law enforcement agencies would then do what they deemed appropriate.
Gutts said the FBI had no persons on any watch list as being likely persons to make threats or do harm. He also said there was no specific evidence of any threat against any jewish organization or other target. the warnings were just general.
Seattle Police say they will have a larger presence at area synagogues and other Jewish organizations and are asking other area law enforcements to do the same.