Who Shot Johnny Rock?

You're supposed to find out who shot singer Johnny Rock (or at least who hired the guys who shot him) and put them behind bars.

The gameplay involves blasting your way through henchmen and bosses, using a tommy gun that doesn't need reloading. However, you have limited ammo and must buy more at times. Your progress is measured by money, and each time you die, you lose some cash. If you run out of money, the game is over.