Why was Erin killed in Mare of Easttown? The motive is the finale's cruellest reveal

Five years on, Mare of Easttown still holds the belt for Most Devastating Answer to a Whodunnit, and it 's not because the killer was shocking (though he was). It's because the why is the single saddest sentence you can type: a kid killed Erin McMenamin to keep his family together, and in doing so blew it apart forever.

The reveal, in case your trauma needs a refresher

After a penultimate episode where Billy Ross confessed and everyone briefly exhaled, the finale revealed that the shooter was Ryan Ross (Cameron Mann) — the teenage son of Mare's best friend Lori. Per NPR's breakdown, the chain of events went like this:

• Ryan discovered his father John was the father of Erin's baby, DJ.
• John had already had one affair that nearly ended his parents' marriage — so Ryan knew exactly what this secret could do.
• When Erin threatened to tell the truth, Ryan posed as John over text, arranged a meeting, and stole Mr. Carroll's gun.
• He only meant to scare her. They struggled. He shot her.

Then John and Billy covered it up, Billy volunteered to take the fall, and Lori — knowing everything — protected her son. The whole family calcified around one child's catastrophic five minutes.

The cruelty is the point (lovingly)

Creator Brad Ingelsby, who wrote all seven episodes, told ET the destination existed before the journey did:

"I had the ending in my head even prior to writing the opening episode."

He also walked Slate through the construction of an ending that made sense in retrospect but stayed unguessable in real time. The knife-twist is thematic: Mare, a mother destroyed by losing her son, has to arrest her best friend's son — and the boy's motive mirrors everything the show is about. He wasn't a monster. He was a scared kid trying to hold his family's shape with his bare hands. That's why it still hurts. That's why we rewatch it anyway. We are not well.