> At the junction of Fremont Street and Victoria Park Road in South Hackney, close to his home, Inspector Neil Sharman and PC Kevin Fagan, the crew of a Metropolitan Police armed response vehicle challenged Stanley from behind. As he turned to face them, they shot him dead at a distance of 15 feet (5 m).

While it may have been an accident, it was a negligent accident. If I accidentally killed someone with a gun I would go to prison. In addition they were found guilty by the jury. It was overturned due to political pressure.

https://en.wikipedia.org/wiki/Killing_of_Harry_Stanley