Conspiracy believers simply start with their conspiracy belief ("Oswald couldn't have done this!!") and then select that information that supports their theory. This is, they reverse engineer a theory. Theory first and then fit the facts to support that theory. The assassination, then, is really a mirror, a Rohrschach test that reveals who the conspiracy believer disfavors.
It's why there are so many different theories as to who was behind the act: viz., the CIA, the Pentagon, the mob, anti-Castro Cubans, Birchers, the Mossad, LBJ, rich Texas oilmen, Castro, the Soviets, the South Vietnamese (for the killing of Diem). It's a long list. Heck, they can't even agree on a basic question as to who Oswald was.
Why are there so many widely different theories after 60 plus years? Conspiracists never seem to want to ask that question.