Best said the alleged offenses varied from assault to arson, destruction and looting.
"The priority is protecting life and ending the destruction. At this moment we know multiple officers and civilians have been injured," she said.
"The Seattle Police Department was prepared to facilitate the peaceful exercise of First Amendment rights. In the aftermath of the murder of George Floyd we all are rightfully angry, sad, frustrated, and heartbroken," Best added.
But, she said, what began as a peaceful protest became violent and destructive because of certain groups who wanted to take advantage of the situation.
Police were still addressing several groups of offenders who continued to assault officers and loot the downtown core, Best said.
The National Guard is also assisting.