SALEM, Mass. (AP) — The latest on the trial of a Massachusetts teenager charged with raping and killing his high school math teacher:

A prosecutor in the trial told a jury that the boy went to school on the day she died with a “terrible purpose:” to kill his teacher.

During opening statements in the trial of Philip Chism, a prosecutor calmly described Chism’s movements on Oct. 22, 2013. She said Chism came to school with a backpack containing a box cutter, gloves and a mask. She said Chism followed Colleen Ritzer into the girls’ bathroom after school, then strangled her, cut her throat with the box cutter, raped and killed her.

A lawyer for the Massachusetts teenager charged with raping and killing his high school math teacher told a jury that he killed her and “did unspeakable things to her body.”

Philip Chism was 14 when ninth-grade Danvers High School math teacher Colleen Ritzer was found near the school with her throat slit.

He is now 16 and being tried as an adult in Essex Superior Court in Salem.

Chism’s lawyer, Denise Regan, began her opening statement Monday by telling the jury, “Philip Chism killed Colleen Ritzer.”

Regan said Chism, who had moved to Massachusetts from Clarksville, Tennessee, was “severely mentally ill,” and had suffered from a psychotic disorder since the age of 10.

He has pleaded not guilty. His lawyer has indicated she will use an insanity defense.

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