You make the claim that he was there, so it's up to you that he was.
Sorry Martin ALL the evidence, from Oswald owning the rifle, Oswald's immediate flight from the scene of the crime, Oswald killing Tippit, Oswald attempting to kill more cops as he resisted arrest through to his multitude if lies while being interrogated, is conclusive evidence of Oswald doing the deed, therefore the burden of proof is on you to prove that Oswald wasn't on the 6th floor at 12:30 on the 22nd of November 1963!
Well, waiting....Zzzzz...
JohnM