On top of all the other evidence provided by other users and the clues I think it is Walter.
In one episode, near the end, Walter bumped into Jane. To me this looked almost on purpose. Then the following (or such) a dialogue occurred;
JANE- Do I know you?
WALTER- No, but I definitely know you!
Yes this could be the fact that Jane, in the storyline, is quite well known, but it is just the way he said it.

Also, I have gathered evidence from the 5USA advert for the new series. In this advert, you can see Lisbon was killed by red john, but the way he (presuming) treated her body was different. In sted of his usual smiley on the wall, he drew it on her face. This is not unnatural for him as one of his first victims had their toe nails painted. However, there is onefeature that is inconsistent. The eyes are drawn as vertical lines on Lisbon and in all the other smileys they are horizontal. If you are not familiar with this advert, I urge you to look online an see what I am on about. this and the fact he slept with Lisbon may indicate special treatment due to a previous encounter.

I was intrigued about HelsMashburns theory so I did some digging and it is probably true. Read it.

this man also satisfies all the criteria/ clues given on this website. As to the "can do a high pitched voice" thing; he can do that (I can't remember what episode).

Finally, he slept with Lisbon which means he can be seductive and lure people and control them. This is exactly what red john does.

PS. he seems to be the only one who calls Jane,  Patrick- like red john