Let's break down the clues...
Has FBI connections= Brett Partridge
Has access to crime Scenes= Brett Partridge
Has access to the CBI Computers= Brett Partridge
Hates Jane= Brett Partridge
Has a voice similar to Red John= Brett Partridge
Is just under 6ft, with straight hair= Brett Partridge
Not sure of his age, but he must be in late 30's or early 40's...important because RJ started killing in late 90's.
William Black also refers to a partridge in his poems
He works the crime scene so if his DNA were to be found he would be overlooked as Red John
Jane considers him a fool and thus not cleaver enough to be Red John
Red John stated that he "hates it when people copy his work" and the only episodes we see Brett in are copy cat killings.
In Epi one he walked in and said "Red John Enters Here" (as he entered) and then with his hand he traced the smiley face ("by what immortal hand or eye can frame THY fearful symmetry"..."Did he smile his work to see")
The scenes with Brett have been edgy on purpose..he has been played as an arrogant, smug worm that Patrick does not like...so we would remember him for a reason.
Patrick has him listed in his book as someone he shook hands with
He appeared in season one and there was no gaurantee that this should would get picked up so it is likely that the "glimpse" of Red John came in season one...
The only thing that gets me is why HE IS MAR appeared on that wall..
When you look at it closely it dos not say He is Mar...
It says Hell IS Mar...
When you unscramble that it spells very clearly...lle (not H.E) IS Mar
When you unscramble that you get two words...
Ellis Mar
Marelli with an extra S
