Posner and Bugliosi reached the same conclusions as the Warren Commission.
There was no sinister overarching conspiracy. There never was and never will be any credible evidence analyzed and corroborated by professional experts proving that Oswald was part of a larger conspiracy. Ditto with Ruby’s role.
Posner genuinelytried to uncover evidence of a large conspiracy, but he never found any. In his book he debunked and disproved every conspiracy wonk claim, and Bugliosi did the same. There was no second shooter, shots from a “grassy knoll”, no magic bullet, no nefarious suspicious behavior by anyone handling JFK’s body, etc. etc.
When Posner first began research for his book, he believed that there was a JFK assassination conspiracy, and the Mafia was behind it. Except there were no facts nor evidence proving this.
Conspiracy buffs have nothing but suspicions, unproven allegations, anecdotal uncorroborated heresay and extremely amateur sleuth skills. They will never let go of this JFK conspiracy nonsense, they are too invested in conclusions they made a long time ago.
If you think the Warren Commission stuff was legit, I suggest you're not playing with a full deck; or you're part of the problem.
Thank G-d for Trump.
ML/NJ
When I first saw Dealey Plaza for myself I knew all the conspiracy theories were bunk. I stood on the sidewalk and felt like I could have reached out and touched that window where Oswald fired the rifle. No hidden gunman from a grassy knoll. It was all bunk and only Oswald killed President Kennedy.
Occam's razor; the more assumptions you have to make, the more unlikely an explanation is. If you have to write a whole book about it, you have proven the opposite of your stated case.