we know Bertram is working with RJ because he asked Kirkland if Lisbon can be trusted (another suspect of mine) but if you listen carefully in the season 4 finale, when RJ says "you strung me along a good long while, well done" he sounds almost exactly like Bertram  but I don't believe the show would use a character as big as him, and he just doesn't fit the expectations for RJ. he is defiantly an accomplice.