An Anonymous Tipster
Aaron rubbed his forehead, feeling a headache coming on. Perhaps the best course of action regarding the reward was for Aiden, as the anonymous tipster, to tell the police station that he wanted them to hold on to the reward for him until an arrest was made.
If Gray was already in custody, he wouldn't be able to see who picked up the reward and they could send anybody without worry. That could work.
Besides, hadn't Brann Knighton said the reward was for information leading to catching his daughter's killer? He might not give the reward out until after an arrest was made anyway. This shouldn't be a problem.
"Make the call and tell the police that you were a witness on the street and saw someone matching Lacy's description being pulled into a cab and that you happened to catch the license plate. If you tell them where it happened, they'll probably check the surveillance cameras anyway," Aaron advised.