(Spoilers for Mare of Easttown will be found below.)
The season finale of HBO’s massively popular Mare of Easttown limited series airs this weekend, and to be honest, there hasn’t been a murder mystery this compelling and buzzy since True Detective, although by season three, it had lost some of its fun because even the director, Nic Pizzolatto, was discouraging fan theories. No one has been discouraging Mare of Easttown theories, including the cast itself. Angourie Rice, who plays Siobhan in the series, even recently suggested that her favorite theory is that the turtle did it.
To be honest, I have no idea who killed Erin McMenamin, although it seems like the photograph that Erin’s best friend, Jess, handed over to Chief Carter might obviously play into the identity of the killer. On the other hand, that photograph could implicate Dylan — who was so anxious about whatever Jess knows that he threatened to murder her — and yet, Dylan doesn’t figure into the promo for the season finale, for whatever that is worth.
The sixth episode ended while leaving us to believe that Billy Ross killed Erin. It seems like a fairly open and shut case. Billy’s father saw him covered blood on the night of Erin’s murder, and Billy even confessed to his brother, John Ross, that he was the father of Erin’s baby, D.J., and that he murdered Erin.
Nothing, however, is ever open and shut in Mare of Easttown, and it would seem odd to essentially wrap up the murder mystery with an episode to go. There are still things outside of Erin’s murder to resolve — Mare’s relationship with her daughter, with her mother, and with the mother of her grandson — but the bulk of the episode is still likely to tie back into Erin’s death.
Personally, I have no idea who killed Erin, but I have read several theories in the last week, and they all seem to center on the Ross family. Here are the most talked-about theories heading into the finale:
John Ross Killed Erin — This one seems to have the most traction and makes the most sense. What we have learned about John Ross (through his affair and his attempts to quiet his son, Ryan) is that John can be very manipulative. Is he manipulative enough, however, to cajole his weak-willed brother into taking the rap for a murder he didn’t commit? The theory here is that it was John who had an affair with Erin, fathered her baby, and murdered her, but somehow talked Billy into confessing, and then he told Lori that it was Billy while knowing that she would tell Mare, further implicating Billy. Additionally, John took his brother on the fishing trip — and put a gun in the tackle box — to kill Billy and tie up any loose ends. Jess’s photograph, in fact, could show John with Erin, which is why Chief Carter called Mare. He wanted to tell her that she fingered the wrong Ross brother. This would also explain by Billy was so angry at John for having an affair, as Billy expressed resentment because John never takes responsibility for his own actions. Could this be yet another example?
Lori Ross Killed Erin — This one is more of a stretch, but this theory posits that Lori killed Erin out of anger because she was having an affair with John (and John is the baby’s father). It’s possible that John knew this, again manipulated his brother Billy into confessing, and then gaslit his own wife into believing that Billy killed Erin instead of her. Perhaps John feels so guilty about fathering Erin’s baby and carrying on multiple affairs that he wants to protect his wife. Billy, in turn, may have moved the body because John had asked him to do so to help him protect Lori. It would also explain why Lori suggested to Mare that Frank was involved; she may have wanted to lead her away from the Ross family.
Frank killed Erin — This was my favorite theory until the most recent episode upended it. This theory suggests that Kevin — who killed himself around nine months before Erin gave birth to D.J. — impregnated Erin. Frank knew about it and decided to help her out with his grandson, but in the process of doing so, Frank ended up having an affair with Erin, too. Erin, in turn, threatened to reveal that secret and ruin Frank’s life if he didn’t help her pay for D.J.’s surgery, so he killed her. It might explain why Frank’s fiance, Faye, is suddenly having relationship problems with Frank. It would not explain, however, why Billy Ross might take the fall for a murder committed by essentially a family friend.
There are some other theories, of course, but none of them make much sense in light of Billy’s confession. Few of those theories, likewise, can be squared with what is potentially on the photo Chief Carter now has in his possession. What we can almost be certain about, however, is that Richard Ryan is not the murderer. He has no motive, and the only reason he is suspicious is that he’s played by Guy Pearce, and we’ve all seen enough Guy Pearce movies to know that could definitely be the bad guy.
We will find out for sure when the season finale of Mare of Easttown airs this Sunday night on HBO Max.