I think we're all looking at this in such a simple way. Nobody knows who Red John is so why would he have to be one person. Nobody said he was one person so maybe he is a name of an idea. 3 people have the 3 dot tattoo which could symbolize the 3 of them that make up Red John.

Between the 3 of them they can have a solid alibi no matter which one of them is committing a Red John related crime.

I think the reason he only made one shot is because out of the 3 of them only 1 could have killed his wife. The other 2 would probably be left tied up to burn in the explosion.