So we already are two suspects down.
Here are my thoughts on two of them:
Reede Smith - I don't believe its him because Red John would not have gone out of his way too shoot Bob Kirkland... I think it is just way too risky
Gale Bertram - In the season 3 finale, when Patrick gave all the suspects different room numbers Bertram and Craig, were both suspects at this time, and they would have conspired had they known they were given different room numbers, therefore it can't be Bertram
The other three, im still trying to work out.
