An incendiary device found along the route of a Martin Luther King Day parade in Spokane, Wash., was "likely capable of inflicting multiple casualties," the FBI said today.

A city employee found a backpack Monday morning, just before the parade was to start, in a parking lot that was both on the parade route and across the street from a performing arts center that hosted a pre-parade rally. More than 1,000 people attended the parade, according to the Spokesman-Review.

Police responded, followed by the FBI. Several blocks around the parking lot were shut down, and the parade was re-routed. The area was shut down all day, as agents first dismantled the device, using a robot, and then called in hazmat teams.

The FBI said today that the device posed a credible threat. "Subsequent preliminary analysis revealed the backpack contained a potentially deadly destructive device, likely capable of inflicting multiple casualties," the agency said in a statement.

The device was found stuffed in the backpack and wrapped in several T-shirts. The FBI is offering a $20,000 reward for information about the person who left it there.

Republished with permission from TalkingPointsMemo.com. Authored by Rachel Slajda. Photo via KREM. TPM provides breaking news, investigative reporting and smart analysis of politics.