I am so sorry that your Mystic has been missing for so long.

I am not a regular responder to the boards, but I "check them out" as often as I can...anyway.

I am not sure you will get the answer you want from these "people". If you confront them, however nicely, they may not even give an honest answer. I don't picture them the most civilized and honest.
If they haven't seen your Mystic, they may just want to hurt you and say they have.
If they have, they may just lie because they are cowards.
They may not know what color or kind of cat they shoot...they may just shoot and not bother checking it out to see if it is alive, dead, suffering.

Sorry for the rambling...these kind of people just strike a nerve with me too.

I think it is best to check it out (with your husband as recommended) because if you bring in the police at the start (and shooting cats is illegal) they may go in that "self protective" mode and lie about seeing him and all their other activity.

Good luck and I really pray that Mystic does find his way home, safely, soon.