$13 in pocket = no escape plan = he didn't think he would get away = survival instinct kicks in = hey, why not give it a shot = bumps into dumb & dumber downstairs = buh, bye suckers = still famous after all these years = smirk
Do you even pause to consider the logic of your statements before you make them?
If he didn't think he would get away, why would he have taken the time to hide the rifle so carefully? (As Dr. Wrone notes, whoever hid the rifle had to climb over a wall of boxes to get to the spot where the rifle was hidden.)
This is not to mention that none of the people who were near or on the stairs when Oswald would have had to come flying down them saw or heard anyone on the stairs. Roy Truly was running well ahead of Baker, and he didn't see Oswald on the stairs or near the vestibule door.
Moving to the Tippit scene, the first and firm reports of the gun used said it was an automatic, based on the shells found at the scene, and it's very easy to distinguish between automatic shells and revolver shells. The fingerprints that Tippit's killer left near his window turned out *not* to be Oswald's. Two witnesses independently put Oswald at the Texas Theater during the Tippit shooting. The weight of the evidence clearly shows that Tippit was shot no later than 1:10, probably at 1:09, just after Tippit signaled the dispatcher that he was getting out of his car, but Oswald, even if he had speed walked, could not have arrived at the scene until 1:14 at the absolute earliest.
I discuss these and other facts in my revised and expanded article on the Tippit shooting:
https://miketgriffith.com/files/malice.pdf