In some locales, the perpetrator of the original crime will be charged. For example, somebody comes into your home and kills your wife. You chase him out and fire a warning shot and he stops and goes to ground (God knows why) You find out later that your warning shot kills an innocent bystander. This all comes out under investigation. He is charged with both killings.
The likelihood of your scenario is incredibly slim at best...and I dont believe for one second that you will get off scot-free. Yes, the criminal may get additional charges, but you will be charged with manslaughter or negligent homicide at a minimum.