Every Theory About Who Killed Erin on ‘Mare of Easttown’

Adrianna Freedman, Leah Marilla Thomas
·5 min read

You should check out Mare of Easttown on HBO to hear Kate Winslet say “wooder” and live her best sandwich-eating life in Eastern Pennsylvania, but stick around to solve a murder with all the twists and turns and skeletons-in-closets that you desire. Between this show, The Undoing, Big Little Lies, and Sharp Objects, HBO really is in its complicated-women-do-cozy-mysteries era, isn’t it? I love it.

There are a lot of characters in this show, and each one seems to come with a whole laundry basket full of drama, so theories about the murder are likely to change every week. There are also, like…already so many crimes. At the beginning of the series, Mare is asked to work on the unsolved case of a missing girl named Katie. There’s also a peeper on the loose in town who seems to have rattled folks. These are isolated incidents unrelated to the murder of Erin McMenamin…or are they?

Erin was a young mother scrambling to get money to pay for her son to get treatment for an ear infection. In the second episode, we learn that the paternity of her child might be a dark secret someone in town wanted to cover up (yes, this is basically the same plot as The Undoing), and it seems likely that more secrets about Erin and people around her will be revealed as Mare of Easttown continues. Here are the suspects so far.


The first suspect is always the boyfriend, or in this case, ex-boyfriend. Erin’s ex Dylan shares custody of Erin’s child and doesn’t seem to have a great reputation around town. He also lies to the police about witnessing a fight between Erin and his new girlfriend right before she vanished. But did he have the necessary motive to kill her? We may never know because Dylan was shot (and likely killed) at the end of episode 2.

So let’s talk about Dylan’s new girlfriend, Brianna (Mackenzie Lansing). She comes in hot by threatening, catfishing, and physically assaulting Erin for “texting her man” in the first episode. She’s such a likely suspect, which would have made me think she was a red herring until HBO’s The Undoing…when (spoiler alert!) the obvious killer really was whodunit all along. Welp! So don’t count Brianna out, even as we learn more information. Her father, Tony, also seems aggressive and could have been involved.

Siobhan Sheehan

Photo credit: HBO
Photo credit: HBO

Mare’s daughter, played by Angourie Rice (Spider-Man: Far From Home), is one of the last people who saw Erin alive. She seems too concerned with getting out of Easttown to commit a murder, but you never know.

Frank Sheehan

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He’s not just suspicious because actor David Denman played Roy on The Office, promise. If Mare’s ex-husband is secretly the father of Erin’s child and Erin blackmailed him to get the money for their son’s medical bills…that’s what I call motive!

Deacon Mark Burton

We haven’t seen much of the clergymen in town, but the way Mark and Mare’s cousin Father Frank alluded to some after-school program at church that Erin stopped coming to was a major red flag. James McArdle, who plays him, is a theater actor too, which, by Law & Order rules, makes him a suspect.

Richard Ryan

Photo credit: HBO
Photo credit: HBO

Speaking of Law & Order rules of crime solving, the biggest “name” outside of Kate Winslet on this show is Guy Pearce, who plays a seductive writer who just moved to the area. New in town? Murder? Extremely sus. We know where this is going.

Kenny McMenamin

Photo credit: HBO
Photo credit: HBO

With the oh-so-wonderful relationship he has with his daughter (I mean that in a sarcastic way), it truly wouldn’t be a surprise if Kenny turned out to be the killer. Since he isn’t in the mood to pay for any of his Erin’s “mistakes,” you'd think he'd be the number one suspect...

Dylan Hinchey

Photo credit: HBO
Photo credit: HBO

If you thought the show would let the ex-boyfriend/baby daddy get away with not being a suspect, then you need to rewatch the first few episodes ASAP. He clearly resents Erin for keeping their baby, and even allows his new GF (Brianna) to publicly beat her up for it. But given how he’s a pretty good liar when interrogated, it’s never fully clear what his agenda is with all of this.

Father Dan Hastings

Sure, he might be Mare's down-to-earth cousin and a member of the clergy, but remember when he alluded to something being a bit fishy about the after-school program Erin attended? Well, if he's willing to cover up for Deacon Mark's wrongdoings (amongst other things), who knows what else he's been hiding?

Freddie Hanlon and Carrie Layden

Photo credit: HBO
Photo credit: HBO

Yeah...chances are these two aren't necessarily involved. But as we know by now, you can't assume anything, especially because Carrie terrorized Mare while she was dealing with a drug addiction. Not to mention Frankie is good at catfishing people (that is, until he's caught)... so maybe they're more suspicious than we thought?

Lori, Billy, and John Ross

Photo credit: HBO
Photo credit: HBO

I truly hope for Mare's sake that the Ross family isn't remotely involved in the murder. After all, they've been so supportive of Mare, and it seems like Lori truly cares for her friend despite being pushed away so many times. But is there an ulterior motive to being just so dang nice? Say it ain't so!

The Peeping Tom

Did we all just not remember this guy existed?

Want more theories and spoilers for your favorite shows? Yeah. We know you do. You can find all of our TV coverage here.

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