Season 7 picks up where season 6 left off. Mr. Smithers believes he may have shot Burns while in a drunken stupor, and turns himself in. But he is proven innocent later, and after the police asking some suspects, they eventually discover Simpson DNA evidence on Burns...
... this is the season where Bill Oakley and Josh Weinstein took over as showrunners, and they wanted The Simpsons to go back to feeling more realistic, with an occasional outlier.