Bruno Heller says we will be disappointed after knowing who is Red John?
So, it must be something heart breaking...
Now in this photo from the next episode https://twitter.com/TheTirthaGhosh/status/403763602944835585/photo/1

we find Cho sitting in between Rigsby and Van Pelt at the back of a car..just like someone who is accused of a crime is escorted..

It may suggest Kimball Cho is Red John.