A Massachusetts state trooper wiped his eyes while testifying about 16 stab wounds to the neck of a slain math teacher that were allegedly inflicted by a student.

The testimony came Thursday during the third day of a hearing on a defense request to suppress evidence in the upcoming trial of 16-year-old Philip Chism. He has pleaded not guilty to murder and rape in the October 2013 killing of Danvers High School teacher Colleen Ritzer.

Chism's lawyers say he invoked his right to remain silent during initial interactions with police, and his statements to police shouldn't be allowed as evidence.

Trooper Steven Buccheri's voice cracked while testifying Thursday about Ritzer's injuries.

Prosecutors accuse Chism of killing Ritzer in a school bathroom and leaving her body in woods behind the school.