Ray Haffner
https://www.google.co.uk/search?q=reed+diamond+height&rlz=1C1CHIK_enGB498GB498&aq=f&oq=reed+diamond+..........
Reede Smith
https://www.google.co.uk/search?q=drew+powell+height&rlz=1C1CHIK_enGB498GB498&aq=f&oq=drew+powell+he.........
Bret Stiles
https://www.google.co.uk/search?q=malcolm+mcdowell+height&rlz=1C1CHIK_enGB498GB498&aq=f&oq=mal&aqs=c........
Brett Partridge
https://www.google.co.uk/search?q=jack+plotnick+height&rlz=1C1CHIK_enGB498GB498&aq=f&oq=ja&aqs=chrom......
Gale Bertram
https://www.google.co.uk/search?q=michael+gaston+height&rlz=1C1CHIK_enGB498GB498&aq=f&oq=mic&aqs=chr.......
Sheriff Thomas McAllister
https://www.google.co.uk/search?q=xander+berkeley&rlz=1C1CHIK_enGB498GB498&aq=f&oq=xander+berkeley&a.....
Robert Kirkland
https://www.google.co.uk/search?q=kevin+corrigan+height&rlz=1C1CHIK_enGB498GB498&aq=f&oq=kev&aqs=chr....
"Only six episodes have focused on Red John, in spite of him being the show's (and Jane's) main antagonist. He appears to be a Caucasian male of average height: Rosalind Harker described him as being "just under six feet tall (approx 180 cm), with short, straight hair, not muscular but not soft with strong hands." Since his killings date back to the 90s, Red John is probably at least in his late 30s or 40s."
This isn't a theory just some concentrated info to narrow the field. Some above are too tall, short, muscley, scrawny or I'm sure if we look back at the episodes some don't have strong hands as Jane has probably commented on one of their handshakes although not all are shown.
Some of my own eliminations: Brett Partridge- A disciple not RJ, too obvious, theres too much info pointing at him but he'd be the key to informing RJ on Jane when he is AT crime scenes. He could also assist in hacking into the CBI "secure" server but it's likely someone else assisted in the hacking as we don't know how far up the chain RJs disciples go.
Bret Stiles- Intelligent enough, has plenty of followers already including a suspect Ray Haffner but he seems far too old to have been the one who RAN away from Cho and Rigsby in the season 1 finale.
Reede Smith- Don't know enough about him could easily be RJ but with great acting but tbh I think he isn't athletic enough I imagine RJ being like Moriarty in the sense he's a capable fighter...although Jane isn't like Sherlock in that sense. But still from my last point on Stiles I don't think he could outrun Cho and Rigsby
Robert Kirkland- I don't think it's Kirkland because he is far too out in the storyline if that makes sense in the same sense as Stiles and Partridge it's seems to easy like we're being pointed in their direction.
Which leaves Gale Bertram, Sheriff Thomas McAllister and Ray Haffner.
Heller said one of the 7 is definitely RJ I personally like all 3 for it.
My favourite would be Gale Bertram although he is taller than 6ft but I don't know if Heller will stay to that fact as the witness was blind.
