Pupil Harvey Willgoose, 15, was brutally stabbed to death by fellow student Mohammed Umar Kahn at their Sheffield High School following a fallout between groups

Harrowing footage showed the moment killer Mohammed Umar Khan played with a knife in the grounds of the same school where he would later fatally stab 15-year-old Harvey Willgoose.

The sickening video was recorded by Umar Khan, who could be seen holding the short blade, at the All Saints Catholic high school on September 16, 2024, several months before the brutal attack. It was the first evidence investigators came across that showed Umar Khan had brought a weapon into school grounds.

Harvey was stabbed in the heart by Umar at the Sheffield high school in February 2025. The trial and sentencing of Khan to a minimum term of 16 years laid bare the disturbing details that led up to the killing.

The upcoming Channel 4 documentary series 'Murder Case: Digital Detectives' exploreds the horrendous attack and the digital evidence that led up to the conviction. Digital forensics revealed during the weekend before the brutal killing, Snapchat arguments between Harvey, Umar and their peers escalated and that threats and challenges were exchanged.

A further examination of images on Umar’s phone revealed he enjoyed posing with weapons, including the one that would eventually be used to murder Harvey.

One investigator said the search showed them that Umar had some kind of propensity to carry weapons. Another crucial piece of evidence were pictures that appeared to be of Umar holding knives - one also being the murder weapon.

A search of Umar’s phone revealed a concerning insight into his state of mind, including searches for: “high level anger,” “anger issues medication” and “waiting for someone to swing to I can let out my anger.” It revealed he found controlling his temper difficult, according to investigators in the documentary.

Further searches showed his fascination with weapons, including the terms: “Rambo knife UK”, “Zombie killer knife”, “medieval knife”, and “machete”. The searches showed he had a fascination with weapons and gave an insight into his thinking.

The murder had all spiralled from a previous knife dispute that had divided the group. But evidence proved the fatal stabbing was not a moment of lost control by Umar, it was instead a culmination of month of online escalation, combined with a fascination with weapons and a vulnerable teenager who was repeatedly failed by systems around him.

The Channel 4 programme also goes over information and digital evidence that uncovers how opportunities were missed in the lead up to the tragedy. All Saints Catholic high school praised Harvey as a "popular, energetic and fun-loving pupil who is dearly missed every day."

Harvey's family described his murder as "senseless and avoidable" and said a report commissioned by the school showed too many apparent "red flags" were missed. His mum, Caroline previously shared her family's pain following failures at the school.

She said: "I’ll always be angry by what happened to Harvey, but more than anything, I’m determined to unite people, bring changes for the better.

"I’m determined that no other family should be sitting in court listening to how their child was killed, have to read a report that lays bare how their child could have been protected. I want to use my voice for Harvey’s memory to push for real change."

The episode will air this Thursday at 9pm on Channel 4.