MADISON, Wis. -

A federal grand jury has indicted a Madison man on a charge of phoning in threats to the state Democratic Party's headquarters.

Federal prosecutors charged 61-year-old William Diederich in a complaint in May with using a telephone to threaten to damage a building and kill or injure people with explosives. The grand jury indictment returned on Wednesday formalized the charge.

According to court documents, Diederich made more than 100 calls to the party's Madison office between January and May, the height of the drive to recall Republican Gov. Scott Walker.

Court documents allege that he threatened to blow up the Democrats' office, shoot anyone who ran against Walker and take head shots at Democrats walking around the state Capitol square.

Diederich's attorney said he hadn't seen the indictment and declined comment.