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Haunting footage of a maths teacher's final moments before she was raped and killed show her alleged murderer following her down a school corridor.

The body of Colleen Ritzer, 24, was found dumped in woods behind Danvers High School in Massachusetts in October 2013.

Student Philip Chism, 16, is standing trial charged with rape, murder and robbery.

He is accused of twice sexually assaulting his maths teacher before slashing her throat with a box cutter.

He is later said to have bought a Wendy's meal with the dead teacher's credit card.

Read more:Mum of teenager alleged to have murdered his maths teacher asks for people's prayers

His defence team previously told the court Chism has admitted to the gruesome killing, but was not criminally responsible on the grounds of mental illness, New York Daily News reported.

Security footage shows Ms Ritzer walking through the halls to a bathroom, before Chism - then aged 14 - appears moments later from a classroom.

(Image: Reuters)

He looks around, goes back inside the classroom and emerges with a hood on to conceal his face.

He follows the teacher into the bathroom, putting on a pair of gloves as he enters.

About 12 minutes later, Chism reappears carrying a pair of black pants - the same worn by Ms Ritzer.

As Ritzer's parents watched the footage, the alleged killer stared at the clip, with no emotion, it was reported.

When Chism did not return home that afternoon, his mother reported her son missing.

He was found by police hours later walking along a busy two-lane road.

(Image: Reuters)

(Image: REUTERS)

When asked by officers if he had anything dangerous in his bag, Chism reportedly said yes. Police found Ms Ritzer's wallet and a bloody box cutter inside.

Officer Neal Hovey previously told the court that when he asked Chism who's blood was on it, the student replied: "It's the girl's," adding she was buried in the woods.

The trial is ongoing.