While I don't know who Jean is, there is something that aligns with you theory of the killer being bound- In the sixth lore tablet, "Child"- Asterious meets one of the men sent to kill him, who responds that he's seeking a weapon said to be able to kill an immortal, to free his father of his eternal life (His father still aged, making it torture). what is important here, though, is this line- (https://gyazo.com/74bc7e724cc77ed27260b27fc37881e5).
Later in the passage, Asterion calls himself the "Guardian of Daedalus's home" and that the labyrinth itself is "holy ground- "That in the center of the maze lies a shrine made by the gods themselves. The visual description of the tablet also is describes as depicting a butchered bull at the opening of a temple.
a second tablet- 18- "Skyros" also mentions something along these lines-
(https://gyazo.com/ad2a0e760c122a6d6e40646fe3695fd4).