By definition, a CEO is a leader, has self confidence, is optimistic, and is able to adjust to situations. In my opinion, there are only 3 reasons for a 61 year old CEO to commit suicide.
Read this article: http://bit.ly/sOvpah for a further description of why people commit suicide.
1. He has an untreatable, painful, illness and wants to end life quicker rather than prolong the agony.
2. A member or members of his family died and he can't go on without them.
3. His life is inevitably going to turn for the worse, and he would rather end it than try to adjust to a new, inferior lifestyle.
1 and 2 can be easily proven, and the fact that no one has mentioned them as reasons, leaves the 3rd one. Diamond Foods would do anything it could to stop a drop in the share price, so if it knew 1 or 2 is the reason, they would have said it.
For #3, the most likely reason for having an inferior lifestyle would be to have to go to jail, or live a disgraced life outside of jail. Or maybe he had a gambling problem. Either way, it leads to a likelihood that he committed fraudulent acts with Diamond Foods. Another question is if he had a drug problem, but that also could be easily proven from an autopsy.