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A look at the ground-breaking digital techniques helping police to solve murders. This episode reveals how digital forensics uncovered the months of online escalation of a fascination with blades that led to the murder of 15-year-old Harvey Willgoose. In February 2025, the teenager was stabbed twice in the chest by his former friend Umar Khan in the courtyard of their Sheffield secondary school.

In March 2020, 19-year-old Jaydon McFarlane was fatally stabbed in broad daylight on a residential street in Ashford, Kent, by a man wielding both a zombie knife and a kitchen knife. As detectives began a fast-moving investigation, they discovered how the victim and killer were former friends who had become members of rival gangs, involved in a dispute over counterfeit £20 notes used to buy cannabis, culminating in a terrifying chase through a shopping centre.

How forensic phone analysis led detectives to the murderer of Samantha Holden. In September 2022, Samantha Holden was found dead in her Farnborough flat in Hampshire. There were no obvious injuries, but her arm was pinned behind her back, her underwear was pulled down and her phone had vanished. The last text Samantha received was from an unknown number: 'I am 30 seconds from your door'. The message was sent by Adam Watson, a man with a history of sexual violence against women. But Watson was already on the run. Phone analysis showed he had fled to Brussels on the Eurostar. As his financial transactions offered fleeting clues to his movements, officers knew the trail would soon disappear as his bank account emptied. In a race against time, armed officers were deployed. While Samantha's post-mortem concluded that she had been strangled, would Watson claim that her death was the result of consensual sex gone wrong?

How detectives used digital forensics to uncover the events of the night 19-year-old Matthew Daulby was fatally stabbed after a street fight in Ormskirk in July 2023. A social media groupchat flagged the names of two men who were also recorded talking about the stabbing in a churchyard.