By the time the two magical flares were shot into the air to alert Elric to the fact that they had been successfully rescued, he had witnessed twenty seven hand offs of the ransom payment containing bag. There was no way a normal city guard tasked with tracking the flow of the money would have been able to follow that many hand offs without losing track of the person with the bad or getting caught.
Elric had the thought that most if not all of the actual Red Skys crew had touched the bag by the time he watched two blue blooms of magical energy flash in the night sky. Had the magical flares been red, he would have been pursuing muder suspects and not just kidnappers. A purple one would have been a single that Aora was in trouble, and needed his help dealing with a problem that she was not capable of contending with on her own.