Police have released footage taken by "body-worn video" cameras that have been successfully used to prosecute offenders.
One video shows a man involved in a stabbing sitting on the floor while being questioned by police officers.
He explains, "I robbed him and he didn't give me what I want, so I stabbed him before I leave."
The man was arrested for grievous bodily harm with intent and later sentenced to 10 years in prison.
The footage was released by the Metropolitan Police as it begins a pilot scheme using the "body-worn video" cameras.