They, aka what ever group of people who urge Oswald to do what he was bragging about, for example that group of homos who he was hanging around, Clay Shaw and his merry men. This bunch of cock suckers seem to be only group of people which has been proved to being hanging out with Oswald. Who knows? I find the theory of the Oswald the Stupid being lonely shooter quite possible, and his motivation was 1. hate towards Kennedy 2. his posse which urge him to keep up his word and promises to kill Kennedy. Like I say, there isn't any fucking evidence about anything else.
I might add that these guys are real, even if the movie JFK paint the picture of them look like some bunch of idiots. They did have military connections, own militia compound for Cuban rebels etc. and Shaw was a respected businessman. They also party with drugs, they were part of the gay underworld and Oswald were their pal. I find it quite possible that this group got tired of the Oswald's rant about Kennedy, and urge him to stand behind his words. When he did, they panic and realize that Oswald would spill all the information he has about their connections to Cuba etc. which would have been catastrophe. They have to shut him up, and only way was Jack Ruby, another gay already dying to cancer. What else they could do? What are the odds to stay alive after killing the president? You have 98% change to get shot by the police, but they get Oswald alive. Bad for Ruby and this gang. If you look about this group of Shaw, Ferrie, Ruby and Oswald, first three were gun runners and militants who were making great income by selling guns and training rebels. Oswald was loose gun, stupid bi- sexual who was coming back from Russia, which has always been homophobic society.
Garrison had all the evidence, but he was stepping on the toes of the Warren commission and pointing out their errors, so they spoil his credibility to save their own face. He also had his hate against gay people play too big role on investigation, so he didn't get whole picture right. If we put sexuality aside and look what connect these guys, Ferrie and Ruby were both cancer patients, they have mutual business as gun runners etc. with Shaw and they were all earning good money. Oswald's act was ruin all that and putting them to jeopardy to end up to prison as accomplish of murder of the president, so they get Ruby to save the situation. And how about this: After the murder Oswald was running around the city like he was looking something? Did he call his posse and ask for the get away car and they promise him one, but didn't deliver because they didn't believe he will shot Kennedy. And when he shot his three shot's, first one hit the lamp post, then there was a pause, and then two more shots. Like...aiming moving target trough the scope...shot..what the hell??...and two more shot's in hurry. If you are right handed you use right eye on the sights, so when you are following left to right movement, you don't see the lamp post on your left eye and it will surprise you completely. That takes seconds to overcome, and reorganizing take few seconds before you find your target again. It all fits in the facts