I think that brett partridge is RED JOHN because-
1)rj and brett have nearly same physical appearance according to the one told by the blind girl and the ,little girl on grave yard..
2)brett hates jane .
2)Match his voice with rj's voice in you tube through these links-https://www.youtube.com/watch?v=k26u5EOWWTUfor brett and this-http://www.youtube.com/watch?v=ns_DWnqrEdI for red john and you will see that they have nearly same soft voice..