You can look into all the shady characters around Oswald, but it's a thankless task. You'll end up with a big huge list of people, all connected to each other in some way or another, and somewhere in there there's probably a couple of people with some actual idea of what's in the works. But there is absolutely no way to tell who they are and what degree of culpability they share. More likely than not a whole bunch of the people considered "Whistle blowers" and "conspiracy researchers" after the fact who are pretending to give you the heads up are actually generating more disinformation to muddy the waters.
That's my whole problem with Final Judgment. I like Michael Collins Piper, but he just needs to admit that he really screwed up with that book. It's no big secret that people in the underworld tend to run together. It's all about a wink and a nod, with everybody watching their own backs and waiting for the shoe to drop somewhere. So you can make pretty much any scenario sound half-way plausible. But blaming the assassination of JFK on some group of jewish hoodlums is just a ridiculous proposition on its face, and it tends to undermine one's credibility to maintain such a thing. I'm sure lots of kikes were jumping for joy when it happened. But the simple mechanics of the thing are such that it couldn't have been carried out without the Secret Service being in on it, and you can't pin that on some outside force.
The Secret Service interestingly is division of the Treasury Department, formed after the assassination of Lincoln.
Rather odd that the agency concerned with the nation's finances is also in charge of the personal protection of the President.