A high school student has been found guilty of raping and killing his algebra teacher in Massachusetts.

Philip Chism, then just 14, followed his maths teacher, 24-year-old Colleen Ritzer, into a school bathroom, where he raped, strangled and stabbed her at least 16 times.

Moments earlier she had been trying to engage the new student in conversation.

His lawyers admitted the teen committed the horrific acts, but argued he should not be held responsible for his actions due to mental illness.

A jury decided otherwise and convicted the teen of the rape and murder of the beloved teacher.

In a statement, Ms Ritzer’s family said they were pleased with the verdict, but expected their pain and suffering to continue through likely appeals and future parole hearings.

“The guilty verdict, while the beginning of justice for Colleen, is certainly no cause for celebration as there can never be true justice for the crime committed,” the statement read.

“There remains a tremendous and painful absence in our lives, one that, sadly, can never be replaced.

“Our family enters a new phase in our lives, one that we have no choice but to begin. However, we do so knowing of the remarkable difference Colleen made in her short life, and continues to make in the lives of so many…

“Colleen never gave up, and neither will we. We will not allow her death to define how she is remembered.”

Mamamia previously reported:

Colleen Ritzer smiled and waved as she walked the corridor of the Massachusetts high school in which she worked.

The popular maths teacher had no idea she would be violently murdered just moments later – allegedly by one of her students.

The image was part of the video footage shown to the jury who will decide the guilt of the teenager charged with Ms Ritzer’s brutal rape and bloody murder.

And it’s an image I can’t stop thinking about.

Perhaps it’s the casual way in which the 24-year-old teacher, who had just finished an algebra class at Danvers High School, moved down the locker-lined corridor with no concern for her safety. It was a regular day at school. She had no reason to feel insecure.

Who was she smiling and waving at?

What was she thinking about?

Maybe she was still processing the glowing compliment she had just received from one of her students, who told her she was “such a nice person”. Perhaps she was contemplating her next tweet.

Posts from her Twitter account, full of encouraging messages, geeky maths jokes and reminders to students about tests and homework, abruptly end the morning of October 22, 2013 – the same day this image was taken.

Moments after Ms Ritzer smiled and waved, she entered the women’s bathroom. Philip Chism – then a 14-year-old student – allegedly followed her in there.

Surveillance video shows the high school student following the teacher before he allegedly kills her https://t.co/H2FQSd9ogu pic.twitter.com/cUIOUfhuZe

— CBS News (@CBSNews) November 19, 2015

CCTV shows a figure emerging from the bathroom with a blood-stained hand and holding a pair of black pants.

Prosecutors allege Chism, now 16, raped his teacher and then fatally slit her throat with a box cutter, before placing her lifeless body in a recycling bin and dumping it outside the school.

Chism allegedly told police Ms Ritzer insulted him, though would not disclose exactly what set him off.

“After she insulted me, that’s when I became the teacher,” he allegedly told police.

He allegedly stole the teacher’s credit card and used it to purchase fast food and a movie ticket.

He is now facing charges of rape, robbery and murder – which, if convicted, would see him jailed for life – but his lawyer argues Chism isn’t criminally responsible for the murder because he was mentally ill.

Police say they picked up Chism later that night, still with a blood-covered box cutter and a white wallet in his backpack.

When questioned about whose blood it was, he allegedly replied, “The girl’s”.

Officer Joseph DeBernardo said: “I asked him if he knew where the girl was.”

“He stated she was buried in the woods. I asked if we could help her. He said no.”

That girl was the one in the photo. A woman remembered for her kindness and passion for teaching.

Touching social media tributes from former students speak of how she changed their lives during her short teaching career and how they pay her kindness forward in her memory.

She was dedicated, enthusiastic, destined for great things.

And this chilling image is a reminder of that. A reminder of a life taken unexpectedly and far too early.

Watch the latest news report on the trial here: