Do you believe Oswald did it all on his own?
If you do, I ridicule you.
The evidence he had help is?
About ten or so days before the assassination he goes in person to the FBI headquarters in Dallas to confront the agent he believed was hassling his wife. When the agent is not there he instead leaves a rather provocative note. Someone who is working with others to shoot the president doesn't do that, do they? Why draw attention to yourself at that point? What was he going to do if the agent (Hosty) was there? Loudly confront him?
He retrieves his rifle - not a very good one - the day before the assassination. He apparently didn't test it for the approximately two months it was stored in the garage. Does it still work? He takes four bullets. Is that ammo still good too? But not his revolver. He gets a ride from a co-worker. He goes to the sniper's nest hoping - with no guarantee at all - that he will be alone. He waits for the president to pass by. When will that happen? He doesn't know whether any of this will work. Why not get a safe ride? A better rifle? More reliable ammunition?
I can go on. You know the details. All of this indicates a rather spontaneous last minute act. There is no planning. It's all thrown together hastily with little deliberation.
This seems clear (to me) it's a desperate act by a lone desperate person, with little foresight, little thought of what was going to happen.