The forensics point to the sixth floor window. The majority of witness point in the same direction. The gun found in the sniper's nest was his. His marksmanship has been replicated. Connelly’s wounds prove he was hit by a bullet fired from the rear, that struck someone else first. The doctors who actually worked on JFK agree that the shots came from behind. There are no other spent shell casings, or entry sounds from any other direction, or any other hard evidence of any other shooter.
There is no credible evidence that Oswald knew Ruby. Ruby had no prior knowledge of Oswald's transfer nor any special access to gain entry to the police building. He shot Oswald FOUR MINUTES after finishing his transaction at the Western Union office. Oswald's transfer had been delayed do Ruby should not have even been able to do the deed. The shooting hardly displayed the expertise and planning of a paid killer.
There are wired coincidences and bad luck involved with just about every infamous crime throughout history. That doesn't spell conspiracy.
Also I challenge conspiracy proponents for the same reason I argue with 9/11 Truthers.