This is above and beyond "What if Jack Ruby never shoots Oswald". What if Lee Harvey Oswald managed to avoid initial detection by the police, destroy the evidence that the rifle was his (the photographs of himself with the rifle), hide his fake Selective Service card and never leaves a palm print on the barrel?
In general, he manages to avoid the most blatant forensic and eyewitness evidence of his guilt. Would he still get convicted, or could he avoid it? If he does avoid it, what are the long term consequences?