I would say there is an over 90 % chance that Oswald was guilty of murder and acted alone. But nothing is ever know for certain. And my views, unlike that of most CTers, are subject to change with new quality evidence.
If there was a conspiracy, it had to be a small one. And almost certainly involved Oswald as a knowing member of it. Large-Secret-Enduring conspiracies are astronomically unlikely. Do the math.