Jean-Christophe Grangé the writer of the novel and creator of the show, wanted Jean Reno to reprise his role as Pierre Niémans from the two prior films, but the producers flatly refused, stating he was too old, and thus, Reno wasn't even offered the part, with Olivier Marchal being cast instead.
In Switzerland and France, the series aired in eight two-part episodes roughly 45/50 minutes in length, while in Germany it aired in four episodes a little over 90 minutes long. Moreover, the four investigations aired in three different order on all three channels. Switzerland's RTS Un aired "Le Jour des Cendres/Tag der Asche" first, followed by "La Dernière Chasse/Die letzte Jagd", "Croisade des Enfants/Kreuzzug der Kinder" and "Leçons de Ténèbres/Melodie des Todes", while Germany's ZDF aired "Leçons de Ténèbres/Melodie des Todes" first, followed by "Le Jour des Cendres/Tag der Asche", "Croisade des Enfants/Kreuzzug der Kinder" and "La Dernière Chasse/Die letzte Jagd" and France's France 2 aired "La Dernière Chasse/Die letzte Jagd" first, followed by "Le Jour des Cendres/Tag der Asche", "Croisade des Enfants/Kreuzzug der Kinder" and "Leçons de Ténèbres/Melodie des Todes".
Prior to Crimson Rivers 2: Angels of the Apocalypse (2004)'s release, plans were already in motion for a third film subtitled "Les Armes de l'Ombre" (Weapons of Shadows) to be written by Matthieu Le Naour & Alexandre Coquelle and directed by Florent-Emilio Siri. When this fell through, a plan for a TV series adaptation developed by Pierre Aknine was first announced back in October 2005 for TV channel TF1. Finally this iteration of the project with involvement of original novel writer Jean-Christophe Grangé was announced in December 2015.
Rather than a straight adaptation of the titular novel, the TV series serves as a sequel to it and to the two films which were made earlier (the first of which, The Crimson Rivers (2000), is a straight adaptation and the second, Crimson Rivers 2: Angels of the Apocalypse (2004), an original sequel).