If you watch videos of the aftermath, you can see it was pure chaos at the Dallas police station when they were holding Oswald. They paraded him around right in front of media, they openly carried the rifle raised up in the air in a crowded hallway. They announced publically when they were going to transfer him to the county jail and into the Fed's hands. They were practically giving an open inventation for a public lynching.

I'm always much more inclined to believe in the utter incompetence and stupidity of government than I am in some grand conspiracy.