Without knowing the details, it's hard to give good advice, but here's my attempt based on the little provided. (Although I understand why, if it was truly a crime, you might want to avoid spewing the entire story across the internet prior to legal action.)

If you were a victim of theft, then it makes sense to both email and send an overnight letter so that you have proof for any ensuing legal action. I also suggest that you copy anyone on the letter, with the cc note that you are copying them, that you feel should also be informed.

You mentioned that it is perhaps a criminal matter. I suggest contacting (on the non-emergency line ), your local police / the local police of the airport and ask them for their recommendation/determination of whether it was a criminal activity.....for crimes, they'd be the ones to investigate it and prosecute it after all (not you or AA). For true criminal activity against a third party (you), it's also not AA's decision of whether it should be prosecuted or not.