Warning: This article contains SPOILERS from the True Detective season 3 finale.
The True Detective season 3 finale has now aired, and the killer has been revealed to be... Isabel Hoyt. Coming almost four years after True Detective season 2, HBO's True Detective season 3 has been a return to form for the series as well as creator and lead writer Nic Pizzolatto. And after eight episodes on the air, spanning across multiple timelines, the story of Will Purcell's murder and Julie Purcell's disappearance has come to an end.
It was originally believed that Brett Woodard was responsible for Will and Julie's deaths in 1980, but then in 1990, new information came to light suggesting Woodard was innocent in these crimes and that Julie herself was still alive. But by 2015, no one had solved the case the yet - at least not in its entirety - or found Julie. Of course, it was revealed in season 3's penultimate episode that former patrolman and Hoyt Foods' current head of security, Harris James, was complicit in the Purcell case, and now, audiences finally know who was responsible for everything.
Related: True Detective Season 3 Cast & Character Guide
Isabel Hoyt, the daughter of Edward Hoyt (founder of Hoyt Foods), experienced a breakdown after her husband and daughter died. Then, one day, at a Hoyt Foods event, she saw Julie Purcell and thought Julie looked like her deceased daughter, Mary. Eventually, a deal was struck to allow Isabel to spend time with Julie, which ultimately led to Isabel wanting to adopt her. Then, when Isabel was meeting with Julie and Will in the woods (which is where they were going the day of their disappearance), Isabel tried taking her and Will wouldn't allow it, thus leading to a tug-of-war, which resulted in Will falling back and hitting his head against the rock.
Junius Watts, who's been described throughout True Detective season 3 as a black man with a white eye, ended up setting up Will's body in the cave in the woods, just as Detective Hays discovered early on. But the thing is, Julie actually helped Watts display her brother's body, and from then on, she never made a fuss with Isabel or Watts; that's because Isabel was feeding her Lithium and stories about Isabel being her mother since Julie (who later believed she was Mary) was 10 years old. At that time, Harris James, who had helped the Hoyt family before, buried the story by paying off Julie's mother, Lucy, in 1980.
In the end, the real reason for Will's death and Julie's disappearance was because Edward Hoyt's daughter lost her daughter, Mary, and she wanted Julie to be Mary's replacement. Unfortunately, Will got in the way. Of course, Julie later escaped thanks to Watts' help (which traumatized Isabel enough to kill herself), and while audiences were led to believe that she died from HIV in 1995, it turns out that she, in fact, ended up living a normal life with a boy from her childhood and now has a family of her own.