"We were following the AI leads" is the perfect excuse for parallel construction[1] (evidence laundering).
If Rekognition supports limiting the search to the people in a specific town (or other small group), it might be possible to force someone to be somewhere on the list of matches. That would give bad actors the perfect tool for manufacturing "probable cause".
I've seen how capricious some can be with their work tools. I dated a girl whose dad ran a background check on everyone she dated without their knowledge or consent. I was 19 at the time and it seemed wrong, but reporting one of the higher up police officers in my town who now knew all my details seemed like a freedom limiting move.
It is another tool to justify police action with a low true positive rate.