Reporter Jonathan Brunt contributed to this report.

Lindsey Reiswig and her coworkers got the first indication something wasn’t right Monday morning when a Spokane Police officer came by Auntie’s Bookstore and said they needed to clear the building because of a suspicious backpack across the street. “We basically evacuated all the customers out of the back door. But we were working on inventory so some of us stayed and worked,” she said. “We didn’t think it was going to be anything serious.” Turns out they were wrong. As Reiswig and her co-workers snapped photos of the police robot examining the backpack at the northeast corner of Washington Street and Main Avenue, posting some of them to their Facebook pages, the Spokane bomb squad was coming to a frightening realization. The backpack was equipped with a powerful bomb, positioned to inflict maximum blast damage toward the intended route of Spokane’s annual Martin Luther King Jr. Day march through downtown. “Then we saw the officer in a bomb suit. At that point, we decided that maybe we should back away from the windows,” she said. The FBI confirmed Tuesday that the Swiss Army-brand backpack contained a bomb that could have caused “multiple casualties” and credited Spokane city employees who noticed the suspicious bag and alerted authorities in time to re-route the parade. A $20,000 reward is being offered for information leading to the arrest and conviction of those responsible. “It definitely was, by all early analysis, a viable device that was very lethal and had the potential to inflict multiple casualties,” said Frank Harrill, the special agent in charge of the Spokane FBI office. “Clearly, the timing and placement of a device – secreted in a backpack – with the Martin Luther King parade is not coincidental. We are doing everything humanly possible to identify the individuals or individual who constructed and placed this device.” Harrill wouldn’t disclose specific details about the bomb. But two security sources, who did not want to be named because they were not authorized to discuss the case, told The Spokesman-Review that they received a briefing Tuesday suggesting that the bomb was equipped to detonate by a remote device, such as a car remote or a garage door opener. The bomb apparently also had its own shrapnel that could have caused significant injuries to anyone near the blast. Investigators were also concerned that the placement of the backpack – on a metal bench with a brick wall behind it – would have directed any blast toward marchers in the street. “I think the link to the Martin Luther King celebration and march is inescapable,” Harrill said. “At that point, it falls directly in the realm and sphere of domestic terrorism. Clearly, there was some political or social agenda here.” Ivan Bush, who has helped organize the celebration and march in Spokane for more than 20 years, said news of the backpack’s potential was “just painful to see and hear.” “Man, that’s a sad testament,” said Bush, who works in human resources for Spokane Public Schools. “Here we are in the 21st century and these types of things are still happening. It just hurts.” The whole purpose of the march was to bring residents together to celebrate a man who championed passive resistance, he said. “This community came together to get a street dedicated to Dr. King and thousands come out to celebrate him every year,” Bush said. “When something like this takes place, it’s just painful.” The FBI is working the case with other federal agencies and virtually all local police agencies via the Northwest Joint Terrorism Task Force. Two T-shirts were found in the bag. One reads “Stevens County Relay For Life June 25th-26th 2010” and another shirt reads “Treasure Island Spring 2009.” Harrill said agents have conducted interviews and gathered surveillance of the area but said he could not discuss any potential suspects. Meanwhile, federal investigators continue to investigate an explosive device that was discovered March 23 alongside the Thomas S. Foley U.S. Courthouse. Harrill said agents have not made an arrest in that case. “We don’t know, at this point, of any linkage to any other incident,” Harrill said, referring to the Monday discovery. “We are not aware of any other events that prefaced this event … or threats associated with this device. Nor does it appear to be linked to any other incidents in Spokane or anywhere else in the country. But, that certainly is a focus for us.” Harrill praised the city workers who discovered the backpack. “They were the heroes of the day. They did what we all should do. They brought it to the attention of police,” Harrill said. “They took quick action, rerouted the parade and immediately called for the” bomb disposal unit. Mayor Mary Verner said city officials are doing all they can to cooperate with the federal investigation. “I was struck that on a day when we celebrate Dr. King, a champion of non-violence, we were faced with a significant violent threat,” Verner said in a news release. “This is unacceptable in our community—or any community.” City Council President Joe Shogan praised the people who found the backpack and the officials who defused it. He noted the 1996 bombing of City Hall and said citizens must still be vigilant to prevent attacks. “It would be nice to think that all this kind of activity was in the past, but obviously, it’s not,” Shogan said. “Too often, there’s that attitude that it can’t happen here. Well, it is happening.” A pipe bomb packed with nails and screws exploded outside Spokane City Hall on April 29, 1996. There were no injuries, but the blast blew out a window in one of the doors and sent shrapnel flying into Riverfront Park. Federal prosecutors later indicted white supremacists Chevie Kehoe, of Colville, and Danny Lee, of Yukon, Okla., for the bombing. Both also were later convicted for a 1996 triple murder in Arkansas. The two were accused of working to overthrow the government to set up a whites-only nation. Back at Auntie’s, Reiswig said she and her husband recently adopted a son and they want to raise him to embrace cultural diversity, which was also one of the goals of the re-routed march. “It’s so sad to me that there are people out there who can’t accept that there are differences (in people) and they are wonderful,” she said. “It is very disappointed to think that someone in Spokane was capable of that.”