Red john cannot be a woman like many say. Jared renfrew's message "he is ma" shows that red john is a man as Red John is described as a he.Red john doesn't  believe in god and  he isn't religious. We know this as in season four's finale he tells  jane that " hell does not exist and I won't be punished when I die.  Most people who don't beleive in god often turn to science making Brett Patridge a strong suspect. Brett patridge has only  been seen in episodes where there were copycats of  red john. This is because if he is red johnhe is their to kill them as.He also fits the description given by Rosalind. In season 5 episode 9 we get a glimpse of patrick's note book with the main suspect for red john and brett is at the top. Another suspect for red john is Gale Betrum. This is becassue the assassin sent  by red joohn to kill hightower enters the jote room which only gale knows. We later find out that the assassin carried a rope which she would use to go to the room below whic only O'laughlin knew. Gale and O'laughlin probably discussed about hightower and  realised that they were given two different rooms And the reason the assassin went f to both  Gale's and O'laughlin's room is  because , Gale is red john and O'laughlin works for him or they both work for red john, see in which room hightower was in. Even though Gale doens't fit the description given by Rosalind I don't think it matters as many of the people patrick suspect, we see in his notebook, dont fit the description either like Dean harker who doesnt have short straight hair.