1. Sheriff was no the Red John.
2. The important part happens during the two years ( missing since the sheriff's death)
3. Jane kills the sheriff and allows the others to believe it's over, so he can go after the real Red John. It takes some time to track him , infliltrate his surroundings, and perform his biggest act yet - taking everything he has. His memories, his personality , and his powers - leaving him a mental wreck - the guy who you've seen sitting at the bar on the beach - Roger. Even if he didn't look exactly like Stiles, that's what happens if you take someone's persona and the spark in the eyes away - the most grandious performance of Jane's life. Patrick Jane is a Monster.