What chemical caused Alan Turing's death?

Cyanide poisoning was identified as the cause of Alan Turing’s death. He was found dead at his home in Wilmslow, Cheshire, on 8 June 1954, and the post-mortem concluded that he had died the previous day.

An inquest recorded the death as suicide. A half-eaten apple beside his bed led to the long-standing story that Turing had consumed cyanide through the fruit, although the apple itself was never tested for cyanide. The exact route by which the poison entered his body therefore remains uncertain.

Some historians and biographers have suggested an alternative explanation: Turing may have accidentally inhaled cyanide fumes from an electroplating experiment in his spare room. The apparatus used potassium cyanide to dissolve gold, and his mother never accepted the suicide verdict.

These debates concern the circumstances and manner of death, not the poison named in the medical findings. Cyanide is therefore the standard quiz answer, while claims about the apple or an accidental laboratory exposure should be treated as possible explanations rather than settled facts.