The "cult" mentioned in the documentary refers to the followers and teachings of Michael Woroniecki, a traveling street preacher who encountered Rusty and Andrea Yates in the mid 1990s. Woroniecki did not lead a traditional church with a physical building; instead, he traveled the country in a converted bus, preaching a radical, fire and brimstone brand of Christianity.

The docuseries features interviews with former followers and Woroniecki’s own nephew, Moses Storm, who describe a belief system rooted in total isolation, rigid gender roles, and an overwhelming fear of hell. Woroniecki frequently corresponded with the Yates family, sending cassette tapes and letters that emphasized the "wickedness" of mothers and the idea that children must be saved from their parents' sins. For a woman already suffering from deep psychosis, these messages of eternal damnation were like pouring gasoline on a fire.

Former husband Rusty Yates, who also participates in the documentary, describes how the couple was drawn into Woroniecki’s orbit. The preacher’s letters often criticized Andrea personally, telling her that her "coldness" was a sign of being possessed by the devil. One haunting recording played in the series instructs followers to "conform" and "yield" to a specific apocalyptic program.

Survivors of the group testify that Woroniecki’s tactics involved "isolation cocoons," where families were encouraged to cut ties with mainstream society and even their own extended families. This isolation left Andrea without a support network beyond her husband and her faith, making her increasingly vulnerable to the delusions that her children were "doomed" unless she took drastic action to save their souls.

The Cult Behind the Killer also reexamines the legal proceedings that followed the tragedy. Andrea’s initial 2002 conviction for capital murder was overturned in 2005 due to false testimony from a prosecution witness. In her 2006 retrial, she was found not guilty by reason of insanity.

The documentary highlights a startling revelation from the retrial: a juror admitted that Woroniecki’s teachings, which were introduced as evidence, significantly shaped the jury's understanding of her state of mind. While Woroniecki has never been assigned legal responsibility for the deaths, the series raises urgent questions about the accountability of radical influencers who target the mentally vulnerable.

Now 61 years old, Andrea Yates remains at Kerrville State Hospital in Texas. Although she has the right to an annual review that could lead to her release, she has consistently declined the assessment. According to those close to her, she prefers to stay in the facility where she continues to receive treatment and mourns the children she killed.

Directors Julian P. Hobbs and Elli Hakami emphasize that the film is not an attack on faith but an examination of how a "homegrown brand of apocalyptic teachings" can destroy a family. By highlighting the survivors of Woroniecki's influence, the docuseries warns that other families may still be at risk from similar manipulative groups operating in the shadows of the internet and street ministry