Read Adam's answer, he gives the facts and cites Bugliosi's book.
There is no evidence anyone else did anything. When people do things, there is evidence, meetings, money changes hands, etc.
By the way, did you know the REASON Oswald was confronted by Officer Tippett a couple hours after the shooting was he fit the description of the guy seen on the 6th floor shooting at the president? Did you know that somoene saw a person shooting, described that person to the police, and Oswald was stopped because he fit the description?
Oh, I almost forgot, Oswald shot officer Tippett in cold blood in front of about 12 witnesses, each of who postiviely IDd him, and together they al saw some or all of him walking over to the cop car, shooting him, walking away emptying the revolver and reloading it.
He had that revolver in his pocket when he was arrested in the Texas Theater, well, actually it wasn't in his pocket, he pulled it out and tried to shoot even more cops.
Some patsy, huh?