Each person who has been murdered or attempted murdered committed a sin of some sort.
Fred committed adultery with Hermione
Grundy was a pedophile
Midge and Moose were doing drugs and having premarital sex.
Remember how Cheryl said no one knows what really happened to Clifford or something like that, what if her and Penelope hung him, but he was killed by strangulation, not in a noose, ie, the murders started last season?
And he was a drug distributor so it continues to fit with this theory.
My thought is this is a gateway to the Sabrina spinoff. That this is some vigilante who is trying to rid the world of sinners. Sabrina is a satanic worshipper or something like that, so either it would be the head of her cult or she could be the last almost victim
I haven’t thought the theory fully through, but those are the basics.