The film argues that the official narrative of the deaths (that it was mass murder-suicide perpetrated by the OTS) is false, and that there may have instead been a government coverup involving intelligence agencies.

Critical reception to the documentary was mixed, with some commentators praising it for its clear overview of the history of the group, though several others called it conspiratorial and argued it did not provide adequate proof of its assertions.

[4] Interviewed by 24 hueres several months before the film's premiere, Boisset described the case of the OTS as "one of the strangest and most horrific crime stories known", and that certain "gray areas" in the investigation had not yet been looked at.

It argues that the recovery of cassettes from the rubble by two France 2 journalists after the scene had been destroyed was evidence of a coverup by Piller acting on the orders of his superiors.

The film also asserts that Di Mambro had ties to Charles Pasqua and the Service d'Action Civique, as well as the assassination of Yann Piat and the deaths of the Saincené brothers [fr] which he links to the OTS through a real estate interest.

[7] It first aired on the Infrarouge block (a documentary slot named for infrared light, "for what cannot be seen with the naked eye") on France 2 on 2 February 2006.

[8] Bruno Icher writing for Libération praised the documentary for managing to tell the story of the group, which he described as an "exceptional" case, in a manner that was chronologically understandable.

He also praised it for straying away from the typical media response to the OTS, including copious usage of its own imagery, instead focusing on the investigation's shortcomings.

"[3] Marianne Behar of L'Humanité said the film's thesis was "frightening" but with substance, noting its conclusion as laconic, showing that the "real beneficiaries of the OTS's cultic and lucrative delusions did not die", but that they had "slipped through the cracks of the legal system".

[12] During the promotion of the 2023 documentary series La Fraternité, also about the Solar Temple, Blick said the theories presented in Les Mystères sanglants de l'OTS remained "unproven and speculative".

Describing the film as aiming to explore "gaps" in the original investigation, they noted that Boisset seemed to think that the true perpetrators of the massacre had not yet been brought to justice.

[9] He criticized several specific statements in the documentary, noting that the content of the recovered cassettes found in the chalets actually backed up the mass murder-suicide theory, and the proof of Lardanchet being an intelligence agent being nothing more than a note on Di Mambro's computer calling him a "mole" (which Palisson believed was merely an example of Di Mambro's paranoia).