Ask yourself in what circumstances might a coroner come to a hurried 'suicide' conclusion in the absence of any supporting evidence? Instead of evidence engage in character assassination of 'a man of this type' having 'unpredictable mental processes'? If the coroner did not find any suicide evidence it can mean only one thing: there wasn't any. Furthermore, why would he claim that Turing ate a poisoned apple when it was not poisoned?

Why would Turing's visiting Norwegian friend disappear without trace?

Turing had become a convicted criminal and overnight he turned into a security nightmare: someone with detailed knowledge of secrets but without the security clearance.