I'm sorry to reveal it, but we will never actually get to see Pj killing Rj, because Red John is already dead.

Brett Partridge was Red John, and he was killed by the Tyger Tyger conspiracy, hence why his last words to Lisbon were "tyger tyger". This is the important clue Heller was talking about.

The Tyger Tyger conspiracy pretends that Red John is still alive, and that's why "they" called Pj after the murder of Brett Partridge. Brett's killer (whom is part of the Tyger Tyger conspiracy) was a former associate of Red John.

The TT conspiracy have committed murders under the name of "Red John" before, but the one who killed Pj's family was Brett Partridge. He was the original Red John, the one who killed multiple women before the murder of Pj's family.

Some people may think that Brett Partridge is too young due to his looks, but his character is actually played by Jake Plotnick who is 45 years old (born 1968). If we assume Brett Partridge is about the same age, he would have been about 20 years old when committing his first murder (at the Visualize barn). This also explains Rj's connection with Visualize, and Bret Stiles extensive knowledge about Rj.

The murder of the private investigator was carried out by the TT conspiracy, not Red John.
Hence the sloppy work and the reveal of the three-dotted tattoo.

McAllister's blurt out "it's not what you think" in the latest episode pretty much means that he wasn't involved in the murder of Pj's family. In fact, noone of them have anything personal against Pj, and noone of them were involved in the murder. Everyone in that room is guilty of something though, the Visualize members for keeping Red John's identity a secret since the barn murder.

I might have missed out on some information but don't fear, it will all be explained in the upcomming episodes ( ¦ ))

(For additional information about why Brett Partridge fits to be Red John, take a look in some other theories. I choose not to include such things, because my intent was only prove how he is Red John, despite being dead. Listing everything else would take too much time. Remember, this is not a theory, it's the truth.)