When the "reasonably intelligent" LHO was confronted by police seconds after the shooting and found to be calmly sipping a coke on the second floor he would have recognised, as "most criminals" would, what a godsend that was, the next best thing to a solid alibi. "Most criminals" would instantly realise the way to play it is to hang around and tell everyone he'd been seen on the second floor seconds after the shooting by his boss and the police. Instead he chooses to slip out without telling anyone knowing it would make him the prime suspect. If LHO was the sole assassin he deliberately spurned his golden opportunity of an 'alibi' and chose to incriminate himself. He also chose to incriminate himself by carrying in his wallet false ID that linked him to the murder weapon, something "most criminals" and "reasonably intelligent" would definitely not do. Think about that. He knew he'd have to leave the weapon behind so he carried false ID on him linking him to the weapon.
Lastly, if LHO was the lone sniper he would've took the shot with the limo coming towards him down Houston Street. Put yourself in his position, a clear head shot as the target moves slowly towards you or a shot through the trees as he moves away? If you are "reasonably intelligent" the answer is unavoidable.