SPOKANE, Washington (AP) — A federal law enforcement official says a man has been arrested in the case of a bomb placed at a parade on the January holiday honoring slain black civil rights leader Martin Luther King Jr.

The official, who spoke on condition of anonymity, told The Associated Press that federal agents arrested the man Wednesday and are preparing to search a location tied to the man.

The official requested anonymity because he was not authorized to discuss the case ahead of an official announcement planned later in the day.

KHQ-TV of Spokane reported that federal and local law enforcement officers had surrounded a home near Colville, Washington, about 80 miles northwest of Spokane. Two T-shirts found inside the bomb were tied to that rural area.

Additional details were not immediately available.

The FBI has said nothing about possible suspects, but public opinion from the beginning focused on some of the white supremacist groups that have brought notoriety to the region in the past three decades. The area once served as headquarters for Richard Butler’s Aryan Nations, whose members were lured by the small number of minorities.

Officials for the FBI in Spokane, which is leading the search, declined to comment on the developments Wednesday.

The bomb was found inside a backpack by city workers before the Spokane parade started on Jan. 17. The parade was rerouted and the bomb was defused without incident.

Officials for the FBI described the bomb as sophisticated and designed to produce mass casualties.

The bomb was sent to an FBI lab in Quantico, Virginia, and the agency offered a $20,000 reward for information from the public.

The two T-shirts found with the bomb were tied to Stevens County. One of the shirts was distributed last year at the “Relay for Life” race in Colville. The second shirt — which had the words “Treasure Island Spring 2009” on the front — was from a local theater production in 2009 in the town of Chewelah.

Copyright 2011 The Associated Press.