The trial of a Massachusetts teenager charged with killing his math teacher has been delayed after a judge ordered him to undergo a mental health evaluation.

Sixteen-year-old Philip Chism is charged in the October 2013 rape and killing of 24-year-old Danvers High School teacher Colleen Ritzer. He was 14 at the time but is being tried as an adult. He pleaded not guilty.

Jury selection started this week and testimony was scheduled to start next Tuesday.

Over the past few days he has refused to enter the courtroom, banged his head against a floor and told a psychologist he hears voices and hopes someone will shoot him.

Prosecutors say he's faking it to avoid trial.

The judge on Thursday ordered an evaluation to determine if he's competent for trial, which could take 20 days.