The FBI said a suspicious backpack was found about 9:25 a.m. PST on Monday on a bench at the northeast corner of North Washington Street and West Main Avenue in downtown Spokane.
A bomb disposal unit was called in and neutralized the device. The FBI said in a statement on Tuesday that "the backpack contained a potentially deadly destructive device, likely capable of inflicting multiple casualties."
The FBI has refused to discuss how the bomb was constructed.
"Suffice it to say it was of grave concern," Frank Harrill, special agent in the charge of the Spokane FBI office, told NBC News.
"You could describe it as an improvised destructive device ... or improvised explosive device," Harrill said.
Area workers initially reported the suspicious package to Spokane police. The march was slightly re-routed and delayed because of the bomb scare.
"The three contract workers in the area who were there are unsung heroes," the FBI spokesman said.
The FBI has not established an official motive, but Harrill told NBC News "the timing and placement of the backpack (along the march route) is inescapable."
"At that point, it falls directly in the realm and sphere of domestic terrorism," Harrill told the Associated Press. "Clearly, there was some political or social agenda here."
Why this wasn't wall-to-wall national news Monday I have no clue. This was clearly a domestic terror attack, set by somebody on MLK Day, at an MLK Day parade. No clue on the suspect or their motives, but the intended target and timing says a hell of a lot.
Someone tried to kill people marching for peace on Monday. This is horrendous. I pray the FBI can nail the people responsible and fast. Two things stand out: the intended target and of the attack and the fact that it was stopped. The system worked here, the backpack was found and disposed of and nobody was hurt.
DougJ makes a solid observation at Balloon Juice:
Expect more of this. And remember it’s all coincidence that it’s all aimed at black people, Democrats, and people who work in the federal government.
More on this as the FBI continues the investigation.