Just poking around with it a little bit, I'm no MAMEr......and I don't have a four player MAME cab......
But it looks like it's just the way it shows up in the tab menu screens.
If you modify the first, third, sixth, eighth, ninth and tenth P1 controls and then open the .cfg for CrimeFighters it shows up as Player 4 controls. So to make the game "function" try just changing those particular P1 to match your control panel for Player 4.
I just threw some random keystrokes in there to see how they showed up, since I don't have a 4 player panel to play with.
Make any sense ?
Curious if that makes player 4 playable at least.