SPOKANE, Wash. — A federal judge has ruled that investigation documents that led to hate crime charges against a man accused of placing a bomb along the Martin Luther King Jr. Day parade route in Spokane will remain sealed.

U.S. District Court Judge Justin Quackenbush ruled against motions by The Associated Press, Cowles Publishing Co., and The Seattle Times that the documents should be released.

Those documents detail the FBI investigation that led to the arrest of 36-year-old Kevin Harpham in the case. The charges against Harpham were upgraded by a new grand jury indictment late Thursday which accused him of violating the federal Hate Crimes Act.

Harpham, who has extensive ties to white supremacist groups, earlier pleaded not guilty to federal charges of attempted use of a weapon of mass destruction and unauthorized possession of an unregistered explosive device. The bomb was found and disabled before it could explode.