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Philip Chism, 15, from Danvers, Mass., stands with his attorneys, Susan Oker, left, and Denise Regan, right, as he pleads not guilty at his arraignment on a second rape charge in Salem Superior Court in Salem, Mass., Thursday, Jan. 30, 2014.

(AP Photo)

BOSTON -- A 15-year-old Massachusetts boy charged with killing his teacher last year faces new charges after an assault on a state youth services staffer.

Philip Chism has been indicted as a youthful offender on charges of attempted murder by strangulation, assault with intent to murder, kidnapping, and assault and battery with a dangerous weapon, prosecutors said Wednesday. He could face adult penalties if convicted.

Chism attacked the 29-year-old woman on June 2 after following her into a bathroom at the youth facility in Boston where he was held, prosecutors said. Co-workers stopped him when she cried for help. The woman declined medical treatment.

A message was left Wednesday for his lawyer.

Chism has pleaded not guilty to robbing, raping and killing 24-year-old Danvers High School teacher Colleen Ritzer after following her into a school bathroom in October.