I'm not sure who Red John is, but I do know one thing: trying to make predictions about his identity based on IMDB cast lists for upcoming episodes is basically pointless.

Fans are starting to suspect that Red John has to be either Smith or Bertram, because these are the only two characters who appear in the IMDB casting lists available online.

That is ridiculous, and here's why.

Just look at the cast list for 'Fire and Brimstone', the episode that's due to air this coming Sunday (November 3). There are only four characters currently listed online; one is Bertram, and the other three are gymnasts. Yet we know from television adverts that all the remaining Red John suspects will appear in the episode, as will Jane and Lisbon.

Based on the previews we've all seen for 'Fire and Brimstone', it's obvious that not everyone who appears in the episode is currently identified on the IMDB cast list. 

Therefore, any clear-thinking Mentalist fan should know it's silly to base their predictions about Red John on cast lists for future episodes. Is it fun to guess? Absolutely. But these IMDB cast lists mean almost nothing at the present time.