Not my specialty, but I can help on this. Ruby has been made a part of lots of conspiracy theories, and you are wise to be cautious.

Ruby was a nightclub owner and had some shady connections to organized crime. This, and some odd remarks he made before his death from lung cancer, has allowed some theorists to make him part of an elaborate Mafia plot to kill JFK. The problem with this was laid out by Norman Mailer, in his article The Amateur Hit Man for the New York Review of Books:

We all know his famous story or cover story. He was grief-stricken by the death of JFK, so bereaved that he shut down his strip-joints for the weekend, and was so appalled at the possibility that Jacqueline Kennedy might have to come to Dallas to testify in Oswald’s trial that he decided to shoot the accused—“the creep,” as he would call him. But only at the last moment did he so decide. No premeditation. At 11:17 on Sunday morning, after waiting on line at a Western Union office to send $25 to one of his strippers who was desperately in need of money, he crossed the street, went down the ramp into police headquarters, and ran smack into Oswald, who was being filmed by TV cameras in the basement as he walked with his police escort to a car that would take him to the County Jail. There, imprinting the American mind forever with the open-mouthed expression of the victim and the squint-eyed disbelief of his guards, Ruby killed Oswald. Never before in history was a death witnessed by so many people giving full attention to their television sets. Much of the world now believed that Ruby was a Mafia hit man. The logic of such an inference suggested a conspiracy not only to kill Kennedy but Oswald as well, because he knew too much.

The concept, clear as a good movie scenario, ran into one confusion that has never been resolved: Why was Ruby standing on line in Western Union waiting his turn to send $25 to a stripper while time kept floating away and Oswald might be moved at any moment? The question could not be answered. How many confederates—and most of them had to be police—would be necessary to coordinate such a move?

In other words, it was impossible for Ruby to have gone on a mission. Oswald was a target of opportunity, and could not have been a planned target.

The best history of the Kennedy assassination, and analysis of the theories around it, is Vincent Bugliosi's Reclaiming History. The writing style is hectoring and often irritating, and it's a whopping big book to get through, but it is very comprehensive.

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