The Ruby connection:

Ruby was at the jail house, and was also reportedly seen at the hospital and Daley Plaza, some say he was a lead in the operation.

Yet, when the mob called upon him to be the ONLY one to give up his life for the cause and kill Oswald, he could only get one shot off to the STOMACH? What kind of an incompetent hit man was he? 
You can almost hear the call with his boss;

Boss, Ruby, did you kill him?
Ruby, I think so!
Boss, What do you mean, did you shot him or what?
Ruby, Ya I shot him!
Boss, Did you shot him in the head?
Ruby, Well no not exactly, I shot him in the stomach!
Boss, You never assassinate someone with a shot to the stomach you idiot, well is he dead?
Ruby, I just don't know!!!!!!

One theory is that Oswald was supposed to be shot in the building.

The call from the boss;

Boss, Make sure the team is in place and shots Oswald before he leaves the building.
Team leader, Will do.
Team Leader, What if he somehow sneaks out?
Boss, Then track him down, but first shot a cop!
T.L. Why shot a cop?
Boss, It will just look good!
T.L. Which cop?
Boss, The first one you see will do, and don't forget to throw down one of those fake Oswald wallets.

The wrong gun in the snipers nest theory.

Boss, make sure that you get Oswald's rifle to the snipers nest.
T.L. Will do
Boss, Bob, I know that you hunt on the weekend with that 30.30, don't bring that one up.
T.L. No way, I will get the right rifle in place.

Yet conspiracist say that the wrong rifle was found in the nest.

Dead witnesses theory.

They say that thousands of witnesses were killed yet, the women who got Oswald his job, the guy that hired Oswald and assigned him to work there that day, they guy who drove him to work, and his wife, lived out their years unharmed. These are the people closet to Oswald!

AND BEST OF ALL.

Boss, Do you a have the hit teams in position
T.L. Yes sir, two teams from behind and one to the front, and one in the grassy knoll.
T.L. But Boss, our teams forensics will not be consistent with the forensics of a shot coming from the snipers nest.
Boss, Not to worry, we have a team of doctors on hand at the hospital, and in flight, and at Bethesda, to change any inconsistencies with the body.
T.L. OMG, you guys have thought of everything.
Boss, I even have the autopsy covered, we know those guys to.

And if it had just continued to rain that day, none of this would have happened!