Well, now he was rotting in Azkaban and he had made sure that he couldn’t escape. But Pettigrew aside, Sirius wanted his prongslet to be seen as a hero like his father and himself. He wanted to make sure that his godson would teach those snakes like Malfoy their place and he wanted to make sure that John would be seen like Albus the leader of light, who would protect Gryffindor, Hufflepuff and Ravenclaw against those disgusting Slytherins.