Are you worried that changed Luca's personality forever?
[spoiler=Crypt 4 books]According to The Spirit Within, spirits may not be the minds of the departed, but rather, something created unconsciously by the telepaths themselves. In this theory, a spirit is simply a telepath's internal mental processes manifesting externally. The telepath obsessed with violence conjures violent spirits. The lonely telepath conjures companion spirits. And when the telepath dies, so do the spirits that (he alone) sees.
That means Luca is a reflection of Duvalier's inner personality. When Duvalier desires violence, Luca take a more violent personality. Luca'ra'il isn't a corrupted spirit of a dead person, but rather Duvalier's own currupt spirit. Maybe people will feel less guilty knowing that they didn't change a real person other then themselves.[/spoiler]