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At teen's murder trial, medical examiner describes brutal attack on teacher

SALEM, Mass. -- Prosecutors rested their case Monday in the trial of a Massachusetts teenager charged with killing his math teacher after a medical examiner described the woman's violent death.

Sixteen-year-old Philip Chism is charged with rape and murder in the October 2013 slaying of 24-year-old Danvers High School teacher Colleen Ritzer.

The prosecution rested its case on Monday after calling Dr. Anna McDonald, a medical examiner who testified that the attack on Ritzer was so violent that it was impossible to determine if she was already dead before being attacked in woods behind the school.

Prosecutors say the attack began earlier in a girl's bathroom inside the high school.

Ritzer was at a minimum in the "dying process" during the attack in the woods, and ultimately bled to death from stab and slash wounds to her neck, McDonald said, reports the Boston Herald. She had also been strangled.

Defense attorneys have acknowledged that Chism, who was 14 at the time, killed Ritzer, but they contend he has severe mental illness and is not criminally responsible for his actions.