The incident began at about 5:30 p.m. Friday, when a number of Occupy Seattle protesters broke into the empty, privately owned building in the 900 block of East Union Street, said Seattle police detective Mark Jamieson.
The protesters then decided to hold a benefit concert as a fund-raiser and let other people inside the building.
Seattle police officers then tried to contact the protesters, but the protesters closed and locked the door, then barricaded themselves inside.
While the officers were at the door, some protesters scrambled onto the roof and began spitting on them, Jamieson said. The officers then withdrew.
When the owner of the building was contacted, he said the protesters did not have permission to enter or remain in the building.
At about 3:25 a.m. Saturday, officers again went to the building and ordered everyone inside to leave. The order was repeated at 3:33 a.m.
At 3:41 a.m., officers entered the building through an open door. Once again, officers asked the people to leave, but several of them remained inside and refused to go.
Officers then cleared the building, arresting 16 people who were still inside. All 16 were booked into King County Jail for investigation of criminal trespass, Jamieson said.