Of course not. The poster I was speaking to said Oswald was "truly a terrible shot", and I presented evidence to the contrary. That's all.
From what I'm reading here - no one could account for Oswald's whereabouts after 12:00. But shots were fired at 12:30. I don't find the fact he was calling out for the elevator to go down at 11:45 from the fifth floor to be terribly unusual. I would imagine he would want to create an alibi for himself.