I know this may be strange to some but Red John is seven letters and there are seven suspects. Could it be possible that each suspect has his own red john trait and that there could be a kingpin red john such as brett?
By this I mean that Red John could be seven different people and one of those seven could ultimately control the rest. Those seven could also have their own disciples. To me it seems plausible because RJ seems to know every single fact, and seems unpenetratable which is where having seven people with different skill sets could come into play? Let me know what you think.