☺ His job gives him access to the CBI and allows his to revisit the crime scene 
☺ From the season 2 finale, when Red John's voice was revealed (and similarly displayed in the season 4 finale), his voice appears to be the closest match out of the suspects list
☺ He's been featured on the show since the first episode; Bruno Heller said Red John's name wouldn't be revealed till season 7 (he said "in two or so" seasons during season 5's run) and it would be a "big disappointment"---Brett been there since the start so it'd be a disappointment if he's RJ since it'd be like we overlooked him all this time
☺ He's probably over 30, he has short straight hair, he's white, and he's just under 6 ft (just by looking), all traits of RJ as confirmed by the clues we have thus far
☺ Even though Jane disrespects him, he lets it slide; in the season 5 finale start, he let Jane boss him around, almost like he knew what was going on (like it was planned)
☺ Just random, but the word "red" is incorporated in his name if you move the letters around