1 - He is well-known for being an expert in Electronic surveillance.
Now... it is clear that Red John has been listening to the team's phone calls and has traced their positions all the time (unless he has psychic powers, which we know he hasn't -- the Mentalist is not Lost).
He has always been one step forward, and there is evidence that he knew new information as soon as the team members knew it (because he killed many witnesses at the very last minute - if he knew "everything" well before Jane & Co, why he didn't do the job well in advance?)
He killed Dr. Miller after Patrick left a message on her voice mailbox.
He reached the place where the three copycats were keeping Jane prisoner just a few hours after Jane left a message for Lisbon in which he said he was getting closer to the killers.
....and many other cases.
We've seen Van Pelt bugging and tracing the suspects' phones. Why shouldn't a former CBI agent, EXPERT in electronic surveillance be able to do that?

2 - His name is only a vowel away from one of his aliases: Ray ..... Roy (Tagliaferro)

3 - He is one of the three suspects whose age is consistent with being "some kid" at the Visualize farm in the late 80s when a young RJ painted the red face on the barn. Stiles, Bertram, McAllister are too old to be called "kid" 23-25 years ago.
This leaves us with only Haffner, Smith, and Kirkland. Among them, only Haffner is a known member of Visualize.