Here's the thing, though...wouldn't the guy finish him off with a shot to the head? From what I know, he shot him in the arm, leg, and back.
Leaving cash behind can mean 2 things:
1. Mob hit
2. The shooter panicked and ran off.
Another thing that points to a mob hit is speeding off in a white Lexus. Not many robbers drive Lexuses these days...unless it was stolen.
Either way, if it was supposed to be a robbery, someone knew this guy was leaving with a lot of cash on that day.