Once inside, police say, Naveed Afzal Haq opened fire with two semiautomatic pistols. One woman, Pam Waechter, 58, of Seattle was killed at the scene. Five more women were wounded.
Haq was ordered held on $50 million bail Saturday pending formal charges of murder and attempted murder.
A Muslim from the Tri-Cities area of south-central Washington, Haq, 30, told authorities he was angered by the war in Iraq and U.S. military cooperation with Israel.
"He pointedly blamed the Jewish people for all of these problems," Seattle Police Chief Gil Kerlikowske said at a news conference Saturday.
Muhammad Ullah, a senior member of a mosque Haq's father helped found in the Tri-Cities area and a close family friend, described Haq as a quiet loner with few friends.
In a statement, the Islamic Center of the Tri-Cities offered condolences to the shooting victims and said "we disassociate this act from our Islamic teachings and beliefs."
Seattle police said Haq picked up the two handguns and spare ammunition just days earlier in the Tri-Cities area, and appeared to have targeted the federation after a cursory Internet search for Jewish organizations.
He also was stopped shortly before the shootings in Seattle for a minor traffic infraction, and was cited and released, Kerlikowske said. Haq had a valid driver's license and his actions did not raise any suspicion, the chief said.
One of the women wounded in Friday's shooting - hit in the arm as she shielded her pregnant belly - helped bring the crisis to an end by crawling into her office, calling 911, and convincing her assailant to talk to dispatchers, Kerlikowske said.
"She's a hero in my eyes," he said at a news conference.
That woman, Dayna Klein, 37, was hospitalized at Harborview Medical Center along with the four others wounded.
Jewish Federation officials identified the other wounded women as Cheryl Stumbo, 43; Layla Bush, 23; and Carol Goldman, 35, all of Seattle; and Christina Rexroad, whose age and hometown could not immediately be confirmed.
The 13-year-old girl taken hostage at the beginning of the melee was not shot, police said.
When Haq got on the phone with 911 operators, he identified himself by name and said, "This is a hostage situation and I want these Jews to get out," according to a statement of probable cause. He later added, "These are Jews and I'm tired of getting pushed around and our people getting pushed around by the situation in the Middle East."
At one point, he told the dispatcher he wanted police to call the media and that he had a gun pointed at a woman's head. He said he was acting alone and had not been drinking, court documents said.
The three most seriously wounded women, who had been shot in the abdomen, were upgraded from critical to serious condition Saturday, hospital spokeswoman Susan Gregg-Hanson said. The other two were in satisfactory condition Friday. A nursing supervisor refused Saturday evening to say whether they had been released from the hospital.
Prosecutors have until Aug. 2 to formally charge Haq, county prosecutor's spokesman Dan Donohoe said. They are not yet seeking capital charges, but that could change, he said.
Authorities searched Haq's parents' home and his apartment - both in the Tri-Cities area of southeastern Washington - and removed evidence, including computers and Haq's car, Kerlikowske said.
Police and the FBI are labeling the shootings a hate crime.
Haq entered the King County courtroom on Saturday wearing handcuffs, chains and leg shackles, and a white jail jumpsuit that labeled him an "ultra security inmate."
Before entering, Haq requested through a public defender that he be allowed to not personally attend the hearing, or for him to not be photographed or videotaped. District Judge Barbara L. Linde denied both requests.
Haq briefly glanced at rows of news media in the gallery on his way into the courtroom but otherwise showed no outward emotion.
Colleagues identified the slain woman as Pam Waechter, 58, of Seattle. Waechter, an assistant director at the federation, died at the scene.
"This is just an extraordinary shock. We lost a really wonderful colleague, a wonderful friend. It's hard," said Nancy Geiger, the charitable organization's interim chief executive.
"She was a person everybody loved, everybody enjoyed being with. She was a tireless worker for the Jewish community," said Rabbi Jim Mirel of Temple B'nai Torah, where Waechter was a past president.
Waechter is survived by two adult children, Nicole and Mark, Mirel said.