Like with JFK, who will ever know unless someone comes out with undisputable facts?
I can buy that Ray did it alone. Lone wolves delude themselves into thinking they will be a hero and life will be good after they do something 'grand' like this.
On the other hand: Why did MLK put himself in harms way by standing on the motel balcony? He had to know he was a target. How did Ray know where MLK would be at that precise moment? An inside job?