Last episode of mentalist cleared much of things than it should be i beleive :)
3 dots tattoo is an interesting field of evidence.
im going to start with 5 dots though; 5 dots means many things in many culture.
it could mean 5 things to do with women, i was surrounded with 4 cops, ill never forget prison etc.
only thing that is absolutely common about 5 dots is it's all about prison.
Just like 5 dots, 3 dots has an interesting facts about prison either but it also represents latino origin.
A man who's probably born and raised in south america, who maybe in prison there before could make red john's possible profile. And most clearly its not the first time the serie is giving hidden clues about red john in latin languages such as names apeearing out of nowhere like Carmen Lee. 

So I suggest Red John is Oscar Ardilles who's the only  Latino Character.