Jan. 18, 2011  -- A suspicious backpack left along a Martin Luther King Day parade route in Spokane, Wash., held a radio-controlled pipe bomb that could have sprayed shrapnel at marchers in the parade.

Three parade workers spotted a backpack with visible wires on a bench at North Washington Street and West Main Avenue in downtown Spokane about 30 minutes before the parade was scheduled to begin Monday. Authorities rerouted the parade while officers from the Spokane Police Department's bomb disposal unit worked on the bomb.

FBI special agent Frank Harrill, the supervisory senior resident agent in Spokane, told ABC News that the backpack was "a viable device."

"The potential for lethality was clear," Harrill said. The local bomb squad neutralized the device, he added.

According to an FBI press release, "Subsequent preliminary analysis revealed the backpack contained a potentially deadly destructive device, likely capable of inflicting multiple casualties."

The bomb, described as a small pipe bomb, was designed to be triggered by a radio frequency system, and was directional – meaning it was designed to spray its deadly shrapnel in the direction it was pointed, law enforcement sources said. Aimed at the parade route, it could have caused multiple casualties among the marchers. About 1,500 people showed up for the parade.

The case is being actively investigated by the FBI's Inland Northwest Joint Terrorism Task Force, and the FBI is offering a $20,000 reward for information leading to the arrest and conviction of whoever made the device.

The FBI has released pictures of the bag and two tee-shirts that were in the bag. The FBI is attempting to locate local security camera footage and is also asking individuals who have pictures or video from the event to contact the FBI.