The last “In Dallas” chapter gives us the story of Jack Ruby’s assassination of Oswald. Intriguingly, Delillo spends a good amount of the chapter trying to minimize the role of Ruby in deciding to kill Oswald. First off, Jack Ruby is portrayed as heavily emotionally distraught. He is described as having vomited and crying continuously since the president's assassination. In fact, he can’t even hear the name “Oswald” or “Lee” without becoming distraught and sick once again. Ruby is clearly absolutely devastated by the loss if his president and is willing to do anything to show his patriotism and loyalty to Kennedy. He even “honors” the president by closing down his clubs: “the carousel and Vegas”. While having a strip club closed for him is not the honor Kennedy was probably imagining, to Ruby this is a massive decision, considering that he is heavily in debt to the mob and needs every dollar that he can make from his clubs.
Clearly, Ruby has been rendered unable to function rationally as a result of Kennedy’s assassination. A good lawyer could probably argue that he was mentally insane at the time he shoots Lee. This sets him up perfectly to be manipulated by Karlinsky. Karlinsky is able to exploit Ruby’s emotional state and financial peril in order to essentially force him to kill Lee. First off Karlinsky spins a tale of how Ruby will he hailed as a hero by the city of Dallas. He says things about how people want to see Lee killed, how Ruby can be the hero of Dallas and save the name of the town. He claims that people will consider the man who kills Oswald “the bravest man in America.” Having manipulating Ruby’s well-known desire for attention, Karlinsky even tries to claim that he will be acquitted in court, as people in Dallas are somehow holding on to the old-west style of justice. He then seals the deal by announcing that Ruby's loans will be forgiven if he does this. His manipulation is so insanely effective, that Ruby doesn’t even fully appreciate what he is doing. This can be seen in how casual he is about it. In fact, he is almost late to his own crime, as he has to wire $25 to one of his club’s employees. He even takes the time to feed his dog, mere minutes before he commits the murder.
In the end, Ruby ironically ends up becoming a patsy of Karlinsky, just as Lee became a patsy for Mackey and the rest of the CIA agents. I think it's interesting that while Delillo sets up it rather ambiguously on whether Lee is guilty of murdering Kennedy, yet seems to unequivocally pardon Jack Ruby. But maybe this is just how I am reading it, what do you think?