A lawyer for a Massachusetts teenager charged with killing his math teacher said her client has refused to go back into the courtroom because he's "about to explode," before the judge excused the jury for the day.

A judge on Tuesday ordered a recess when 16-year-old Philip Chism refused to re-enter court.

Chism's lawyer said her client was shaking, twitching and mumbling and told her "he's about to explode and … doesn't want to hurt anyone."

Chism has pleaded not guilty to murder and other charges in the October 2013 slaying of 24-year-old Danvers High School teacher Colleen Ritzer. Chism was 14.

His lawyer says Chism killed Ritzer but isn't criminally responsible because he is mentally ill.

Ritzer's mother testified earlier Tuesday about the day her daughter was killed and the search for her when she didn't come home.