AUGUSTA — An Augusta man who has already spent six years in federal prison for the armed robbery of a pharmacy is going back behind bars for another four years for assaulting a man with a hammer.

Zachary Gagnon pleaded guilty Tuesday in Kennebec County Superior Court to aggravated assault in connection with the attack last summer in Augusta as well as possessing heroin when he was arrested on that charge Aug. 11.

Gagnon was sentenced to 10 years in state prison, with all but four years suspended, and three years of probation.

The sentence will run concurrent to the final three years of his federal sentence.

The Kennebec Journal ( reports that Gagnon was freed from federal prison in December 2008 after serving nearly six years of an eight-year sentence.