Your right you probably know alot more about that phych shit than I do.......But a death of his "friend" 2 years later aint gonna have an effect on him killing his family....Like ive said in the past If he was well enough to work entire wrestling matches...and staying professinal and showing no signs of losing his mind,then how could he of had this "brain damage"
No, the death of the friend did not directly cause the death, however there are several scenarios in which the death of the friend can cause a deep enough depression to be somewhat dangerous.
The brain damage can go undetected for years if he doesn't get a CAT scan on a regular basis. Even the subtle social changes can go unnoticed.
Now, I'm not saying this excuses his behaviour, but it does partly answer the question of why.