A Schuylkill County judge has sentenced a state prison inmate who admitted attacking another prisoner last year to at least four years behind bars.

Judge James Goodman imposed the punishment on March 28 on Nathaniel C. Clark, 31. Clark, who was charged with aggravated assault, simple assault and harassment after the May 16, 2013, attack, must serve at least 52 months up to 104 months in state prison.Clark must serve the time in addition to sentences he received for drug-related crimes he had committed in Delaware and Blair counties.According to court documents, Clark was in the state prison in Mahanoy Township when he was captured on video approaching inmate Michael A. Haynes, 39, from the rear and assaulting him. The video showed Clark stabbing or striking Haynes 17 times in the head, shoulder and upper back with some type of weapon.Police said the attack was unprovoked.Prison guards took him into custody and placed him in a restricted cell. Haynes was treated for his injuries in the prison infirmary.