Source: Joseph E. Persicoe's 'Nuremburg: Infamy on Trial'

The idea that Goering was given the cyanide by one of his guards is regarded as the most likely case of affairs. Firstly, Goering's ability to interact with anyone other than the guards was strictly regulated so the guards supplying the drug is the most likely means of him having acquired it. Secondly, its widely ackowledged that Goering was someone who was very easy to get on with and is described as charming by many of the opeople who met him. He was especially able to build relationships with the soldiers because he himself had been a member of the military when he was younger. It's therefore believed by many, and Persicoe's book - as well as telling it as a narrative, the book goes into a detailed discussion of the history and the means by which Persicoe has come to write his book - argues this case, that Goering built up a strong relationship during his incarceration with one of the guards who frequently was stationed with him and that this guard provided the cyanide he used to kill himself rather than be executed by the Allied court.