Gemma then leans in and quietly gives Jax the truth: "JT and Kellan decided to get the MC out of guns, away from the IRA. Clay thought it was a mistake. He was afraid John would destroy the club. So he decided to kill him." Cut to Jax looking shocked by this -- whether it's because he's surprised that Clay actually did this (Ha! He knows Clay'll kill anyone in his way) or because Gemma's actually not lying to him or because he's horrified that his mother is married to his father's murderer? The answer depends on how dumb Jax is during any given episode.
ANYWAY. Gemma explains, "The first time, he sent John into a Mayan ambush, unprotected. Your dad made it out, but he knew it was Clay who'd set it up. And he knew Clay would try again. He predicted it would be mechanical. He was right." Jax finally realizes that JT's fatal accident on 580 was the work of Lowell Sr., acting on Clay's behalf. And as all of you will remember from Season One, Lowell, Sr. was killed a week after the accident and his body dumped in with some Mayan corpses -- something that made no sense given that it was the Mayans who allegedly killed him. And that was how we learned, in Season One, that Clay silenced Lowell Sr. And now, three seasons later, Jax is finally figuring it all out. We can actually see the wheels turning as he processes everything.
Then Jax asks the $1,000,000 question ("How do you know all this?") and Gemma, bless her lying little heart, says vaguely, "The letters, the speculation, the Mayan ambush." Then she hones her pitch so she can really begin to manipulate Jax: because those letters prove that Clay killed JT, Clay would do anything to sit on them. Jax has an a-ha moment and says, "Piney got a hold of these." Gemma replies, "He must have threatened Clay. (Drops her voice to a sorrowful whisper) That's not all. I found the cover letter Maureen wrote telling you to read them. It was in your house. I knew Tara was the one who found them. I -- I panicked. I told Clay."
Over the space of 30 seconds, Jax's face slides from studiousness to incredulity to a barely-restrained rage. Quaking with fury, Jax asks, "Clay knew? That Tara had these?" Gemma confirms, "He tried to kill Tara. That thing that happened at the park? That wasn't the cartel. That was guys Clay hired to kill your wife, Jax." Jax has stopped quaking and he has passed into a frightening place of utter stillness.