Sure of suicide? :
Professor Jack Copeland (philosophy) has questioned various aspects of the coroner's historical verdict, suggesting the alternative explanation of the accidental inhalation of cyanide fumes from an apparatus for gold electroplating spoons, using potassium cyanide to dissolve the gold, which Turing had set up in his tiny spare room. Copeland notes that the autopsy findings were more consistent with inhalation than with ingestion of the poison. Turing also habitually ate an apple before bed, and it was not unusual for it to be discarded half-eaten.[103] In addition, Turing had reportedly borne his legal setbacks and hormone treatment (which had been discontinued a year previously) "with good humour" and had shown no sign of despondency prior to his death, in fact, setting down a list of tasks he intended to complete upon return to his office after the holiday weekend.[103] At the time, Turing's mother believed that the ingestion was accidental, caused by her son's careless storage of laboratory chemicals
From
http://en.wikipedia.org/wiki/Alan_Turing