quarantine 'em

(Several of the suspects did not have access to a firearm. Unfortunately, this clue places them back under suspicion.)

Burns collapses with his hands pointing to the letters W and S on the town sundial. This suggests that the assailant had the initials M. S., S. M., S. W. or W. S..

(Analogue clocks set to 3 o'clock and 9 o'clock throughout the episode have been training us to think about looking at the sundial upside-down.)

It is possible that "S. W." indicates "Smith & Wesson", Grampa's gun which is seen earlier, and to which numerous characters have access - but only one shot was heard, and we already ruled this firearm out, above.

At this point in The Simpsons' run, there are several characters who definitely had these initials (and who appeared in this episode): * Waylon Smithers * Marge Simpson * Moe Szyslak (his surname was revealed for the first time in this episode) * ...

* Principal W. Seymour Skinner (first initial revealed for the first and only time in this episode) * Sideshow Mel * Santa's Little Helper (whom Burns refers to as "Simpson mutt" earlier in the episode) * Maggie Simpson

Still with me here? * Smithers has a cast-iron alibi - he was watching "Pardon My Zinger" at 3pm * Marge is on camera at the time of the shooting. This is enough for us as viewers * Sideshow Mel's weapon of choice is a flick-knife, which potentially rules him out as a shooter

Now let's re-examine the town hall seen. "Oh, you all talk big," Burns says, "but who here has the guts to stop me?"