One day, while under the influence of alcohol, Harry had wished Cassandra was dead. Not long after, on the night of the prom, Cassandra was murdered. In Putting on the Clothes, it was revealed by Harry that Dewey had confessed the murder to him, expecting a thank you.

Why did Dewey shoot Cassandra?

It's revealed that Dewey — who, tbh, up until this point didn't have much to add to the show — killed Cassandra in hopes of making Harry (Alex Fitzalan) happy. ... With a few gunshots, Cassandra falls to the ground and dies from her wounds.

Who killed Cassandra in the society theory?

But at the end of Episode 3, fans were shocked when Cassandra was shot and killed outside the kids' makeshift prom. As Allie, Gordie (Jose Julian), and the Guard began investigating her death and confiscating guns, loner Greg Dewey (Seth Meriwether) essentially confessed to Harry (Alex Fitzalan) that he shot Cassandra.