A viewer told KHQ that "at least nine FBI vehicles sped towards a house near Highway 395 south of Colville. At least two counter-assault vehicles were also at the house."
In January, the FBI said the bomb was left in an act of "domestic terrorism," but did not have yet have a motive identified.
"Clearly the confluence of the parade route, the timing, the fact that the device was likely placed on that route roughly an hour before the parade ... falls squarely within the realm of domestic terrorism," Frank Harrill, the special agent in charge of FBI operations in Spokane, told TPM at the time.
Later in January, Spokane County Sheriff Ozzie Knezovich told a reporter that the bomb had some sort of chemical in it.
City workers found the bomb in a backpack half an hour before the parade began.
A FBI spokesman in the Seattle office referred questions to the U.S. Attorney's office, which did not immediately respond to a request for comment.
Late Update: The Seattle Times reports the suspects "are apparently affiliated with white supremacists."
An FBI source in Washington D.C. told the Times one man was arrested east of Spokane, and agents were preparing to search a home where other people with connections to the suspect live.
Additional reporting by Ryan J. Reilly
Correction: this post originally said the bomb was found three hours before the parade.