Well,im no expert nor have i seen this show from the very beginning,thus i do not have all the facts at my disposal. However i have watched from season 4 and i have come to the conclusion that lisbon is either Red john or is in some way involved with him/her. The latter is the most probable case becasue she does work really close with patrick and he trusts her. Hence she is Red john's most probable informant.
But i may be horribly wrong............ who knows?
