What do bodies found in the morning on different places in Toulouse have to do with the lyrics of a Claude Nougaro song?

What do bodies found in the morning on different places in Toulouse have to do with the lyrics of a Claude Nougaro song? Having to solve this case are Captain Simon Keller, an old man who hasn't been spared by life, and young Cécile Gimet, just out of police school - who happens to be on her first field investigation. Weakened by disease, Keller make a point on closing the case as soon as possible, while Cécile will realize this story will make the painful secrets of her childhood resurface.—Happy_Evil_Dude

Police commander Simon Keller, teams up with Cécile Gimet, a young recruiter who just left police school, to investigate the murder of a man found in the Basilica of Saint-Sernin in Toulouse. The victim is identified as Sebastian Barel. The body of his friend, Franck Letellier, is found at the Capitole square. The investigators learn that both victims were the members of the same band called Jupiter. They track down the other members including Cécile's uncle Frédéric Gomez, and Jérôme Dottin. Frédéric is poisoned, but luckily Cécile arrives in time to save him. Dottin's body is found in the Canal du Midi. They come to realize when Cécile's father Gomez, also a member of Jupiter, showed some lyrics he composed to the famous singer Claude Nougaro, Nougaro praised his talents and advised him to go to Paris. But the other members of Jupiter were pissed off and tried to talk him out of leaving Jupiter. While they argued, Dottin shot Cécile's father by accident. They all agreed to fake his suicide and threatened Serge Blondin, the police officer in charge at that time, to falsify the report. Now that Frédéric knows the truth, he takes revenge on them all, placing their bodies in places according to the lyrics of Nougaro's song Toulouse. He even poisons himself to avoid suspicion. And now it's Blondin's turn to die. The investigators arrive in time to stop him.