A "potentially deadly" explosive device that could have inflicted severe casualties was found along the intended route of a Martin Luther King Jr. Day march in Spokane, Wash., a half hour before it was to begin, the FBI said Tuesday.
The annual Unity March was rerouted for safety after city workers noticed a suspicious black Swiss Army backpack apparently abandoned on a bench about 9:25 a.m. PST Monday, said Frank Harrill, the supervisory senior resident agent in the FBI's Seattle division.
The device inside "clearly would have had the potential to inflict multiple casualties, injury and death, to humans," Harrill said in an interview Tuesday. He declined to describe the device.
The FBI said the backpack also contained two T-shirts -- one from the 2010 Stevens County Relay for Life and the other reading, "Treasure Island Spring 2009."
About 1,500 people marched along the new route without incident while the Spokane Explosives Disposal Unit neutralized the explosives.
No group or person has claimed responsibility or offered a motive, Harrill said. But he called the connection with the Martin Luther King Day march "inescapable."
"We're treating this as an act of domestic terrorism," he said.
The FBI, which is leading the investigation, is offering a $20,000 reward for information leading to the arrest and conviction of those responsible.
The area has a history of white supremacist activity. Until 2001, the Aryan Nations was headquartered in nearby Hayden Lake, Idaho. As recently as April 2009, the Spokesman-Review newspaper reported that residents of a Coeur d'Alene, Idaho, subdivision had found Aryan Nations recruitment letters on their lawns.
Ivan Bush, who works for Spokane Public Schools and has helped organize the King Day march for more than 20 years, said the attempted attack pained him.
"Man, that's a sad testament," Bush told The Associated Press. "Here we are in the 21st century and these types of things are still happening. It just hurts."