ok, so my theory is that Marge Simpson was the one who shot Mr burns my reasoning is that everyone in her family had been bothered by burns Lisa losing her favourite classroom, Bart's dog being injured and also his treehouse was destroyed etc. I think that marge was so enraged by this so much that her anger took over and she shot him.the reason Mr Burns said Maggie had done it is because in season 4 episode 7 he fell in love with marge and still has love for her.he told the police it was Maggie because realistically they can't really send Maggie to jail and he saw it as the easiest way to let the Simpson family go home free. Also because come on, the baby could they even carry the weight of a gun without falling over. It was almost as big as the baby itself. that's like asking a grandma to carry a fridge.