It needs to be accepted that no-one in the list of seven is in fact Red John. At the moment the show has two main issues which require resolution:
1. Who is Red John; and
2. What is Tyger Tyger.
The nature of the show is such that these have to be interrelated. So, a third question requires resolution as to how they are connected. This theory will seek to address these three issues.
Firstly, it is suggested that Tyger Tyger is a group either controlled by Red John, or which Red John is an individual (senior) member of. It has been shown that members of the group have no qualms about killing, so either would fit.
Secondly, the first point has largely answered the second main question. Tyger Tyger is a group of law enforcement personnel who have been brought together for a common goal. What that common goal is is unknown. However, it is submitted that it is likely to do Red John's bidding. This explanation would very simply explain how Red John seems to be an omnipresent, omniscient, phantom-like person, who never leaves a trace, who never fails, and who possesses a skill set almost unbelievable in breadth and depth. Red John as a controlling force also explains why so many people are willing to abandon the oaths they swore when taking up their jobs - it cannot be denied that he is charismatic, if nothing else.
Who is Red John? This, as one would expect, is the biggest conundrum. However, several points can be made about this:
(a) all evidence as to identity should be regarded as unreliable.
No evidence has ever been separately corroborated. Thus, facial descriptions, voice descriptions, height descriptions, phobias; everything, could merely be the traits of a multiplicity of servants working for Red John.
This means that the list of seven, derived from Lorelai's comment, could mean nothing; it could mean that the list is useless. It is clear that the tattoo is nothing special, as three of the above seven have them, as do many more people.
The point is, that someone as cunning as Red John would be more likely to deliberately plant evidence that to make so many vital mistakes.
(b) The reveal has to be shocking
The build up to this has been immense. To merely reveal Bertram, the Sheriff, or even Partridge would be anti-climactic.
Further, as stated above, the nature of the evidence revealed is such that it would be entirely plausible for it to be another person.
(c) Who planted the bomb?
If it was one of the six people in the room at the time, then Red John is either very confident of his physical ability to withstand a blast, or was not there. This means, the bomb was planted earlier and RJ escaped, the bomb was carried in by one of the 5 and RJ escaped, that RJ is not one of those people, of PJ planted it. All are plausible.
(d) Some possibilities
I know that many people are reluctant to state that one of the CBS team is RJ. However, it is submitted that this is very likely, or it is likely that someone who has been involved from the very start has been involved. It must be remembered that this reveal has been years in the making.
It would make sense for RJ to be a master puppeteer, controlling an entire scene from the background, with the stinger for PJ that they were along for the ride the whole time. So, we need to find out who controls Tyger Tyger and I think we have a strong candidate... this is not any of the three list suspects with tattoos - they are soldiers.
(d) Does PJ know more than he lets on?
It is a very real possibility that PJ has known from very early on who RJ is, but is playing a very long game (ten years) to ensure that he can catch and kill RJ, and/or do as much damage as possible to him/her.
(e) The solve
To solve the mystery, it needs to be ascertained who has been in the show from series one. All the regulars, including van pelt, fit this bill. So, it could be, Cho, Rigsby, Van Pelt, Jane or Lisbon. Of these only the former three are likely, and of those van pelt is the most obvious. She is very clever, has red-hair, and has the computer-smarts to pull it all off electronically.
Of the three suspects listed, one approach would be to identify the appearances of RJ in person, and see where they were, and what they were doing. It is suggested that at least some kills attributed to RJ would be personal kills, so an absence at such a time might raise suspicion.
If it is not a main character one could go through the cast for each episode and see whether there are multiple appearances from a person who isn't main. Hopefully Heller was setting this up the whole time, so there should be easter eggs to be found. It is also possible, though unlikely, that some people have not been named for their role to prevent this.
The upshot. Stop focusing where we are being told to focus, and think outside of the box, just like RJ and PJ do.