He didn’t have to. Just a wink and a nod to the leader of one of the five families, and they send out a torpedo to hire a punk to do the deed.
That is the problem. Once the punk starts shooting and people start grabbing at the gun and arms bullets fly in all directions.
Cermack was whacked because of a local dispute between his allies in organized crime and the Capone gang although there really much real information out about this.
Since FDR was sure to repeal Prohibition I don’t see how the Mob could want him to be elected.