The Season 3 finale of 13 Reasons Why left fans with a ton of pressing questions, and theories have been rampant regarding one major twist specifically. One of the most prominent fan theories makes a pretty convincing case on explaining that vague character ending. Spoiler alert: This post contains spoiler from the 13 Reasons Why Season 3 finale. Monty's sudden, off-screen death in the finale threw most fans for a total loop, but now viewers think they may have figured out what happened to him. Did Seth kill Monty in 13 Reasons Why? That's the new theory the fandom is buzzing about, and honestly, it could make sense.
Monty's death is definitely the biggest mystery that viewers were left with at the end of 13 Reasons Why Season 3. To be honest, it felt like it kind of just happened out of nowhere, and the circumstances go wholly unexplained. In the final episode, Ani mentioned she heard through the grapevine that Monty had been killed in prison shortly after his arrest for sexual assault, and she and the rest of the gang proceed to frame the now-dead Monty for Bryce's murder (which was actually committed by Alex). However, fans never found out who actually killed Monty, nor did they see his death on-screen. This has led some fans to buy into theories that Monty could still be alive, but another prominent theory is that Seth was the one who killed Monty... and the Liberty High students may have orchestrated the murder.
In case you don't remember Seth, he is Justin's mom's drug dealing boyfriend, whose abusive behavior drove Justin out of his home. In Season 3, Seth returned to force Justin to sell drugs for him, but ended up getting arrested toward the end of the season. Suspiciously, soon before the arrest, Justin was shown asking Seth to do him a favor in exchange for him returning to selling drugs.
A popular theory on Reddit guesses that Justin may have gotten Seth to kill Monty in prison so that the arrested jock could not defend himself when the group framed him for Bryce's murder. Honestly, Seth does seem like a fitting suspect for Monty's murder, since he was apparently in jail at the same time as Monty.
However, while Seth may very well have been the one to kill Monty, there are some holes in the theory concerning Justin's potential involvement. First, Justin had previously revealed that the favor he asked of Seth was to get rid of the dealer Justin met up with on homecoming night, so that he could come forward as an alibi for Clay. Plus, Justin almost definitely could not have known about the plan to pin Bryce's murder on Monty prior to Seth being arrested. On top of all that, as another Reddit user pointed out, there is really no benefit for Seth in murdering Monty, and it's highly unlikely that he would follow Justin's orders without getting something big in return.
Of course, this theory hinges on the idea that Justin — and perhaps more of his Liberty High friends — would go so far as to plan the murder of one of their peers. Could they really have taken their antics to that level?
Regardless, Seth does seem like a convincing choice for Monty's murderer, whether Justin was involved in orchestrating the kill or not. Fans will just have to wait until Season 4 to find out if this theory proves true.