Police are working to determine how many shooters were involved in the fatal incident near Pike Place Market.
Brown is facing charges after him and his trainer were accused of battery this week.
The three men who died in the crash in Australia were identified as residents of Montana, Arizona and Florida.
"Make no mistake, this is an emergency in China," the director-general of the WHO said.
The State Department said extraditing Anne Sacoolas, who was covered by diplomatic immunity, would set a troubling precedent.