(ABCNews)-- A Massachusetts teenager charged with the murder of a popular high school math teacher sexually assaulted the woman in what a prosecutor said was a series of "unspeakable acts" in a brutal assault, according to an indictment released Thursday.
An indictment released Thursday charged Chism with murder, aggravated rape and armed robbery in connection with the savage attack, Essex County prosecutors said.
The teenager is slated to appear at Salem District Court for a court hearing Friday.
Chism allegedly raped Ritzer "with an object" and stole her underwear, iPhone and credit cards after the murder, said Essex County District Attorney Jonathon Blodgett said in a statement.
"The indictments returned today detail horrific and unspeakable acts," Blodgett stated. "This is the first step in a long process to secure justice for Ms. Ritzer and her family."
Ritzer's body was found on Oct. 23 in a wooded area roughly 50 feet from an athletic field behind Danvers High School. Her throat had been slashed with a boxcutter and she had been punched in the face, police officials said.
According to court documents, Chism followed Ritzer into a bathroom after he pulled on gloves, an act that was captured on a school security camera. He moved her body out of the bathroom in a blue recycle bin on wheels, the documents state.
He then went home to change his bloody clothes and ate lunch at Wendy's before seeing a Woody Allen movie at Hollywood Hits, a theater not far from his Danvers home which he shares with his mother and two younger sisters, according to police. On the night of Oct. 22, both Ritzer and Chism were reported missing.
Chism was arrested and charged with first degree murder as an adult at 5 a.m. Oct. 23 and Ritzer's body was found a short time later.
Chism pleaded not guilty at his arraignment on the murder charge last month.
Blodgett said Chism will be arraigned on the additional charges of rape and armed robbery but no date has been set.
Chism's lawyer Denise Regan could not be immediately reached.