In criminal law:
In Florida, if you commit a felony, and in the commission of that felony, someone gets killed, it's felony murder. For example, you rob a liquor store and kill a bystander by accident, you're guilty of felony murder. You rob a liquor store and your accomplice gets shot by the clerk, you're guilty of felony murder.
So, if someone committed aggravated assault and the victim defended himself, the felon would be responsible for anyone who was shot. Of course, all the facts have to come out and a jury has to interpret the law and the situation.
In civil law:
Then you really open up a can of worms. You can sue just about anybody for just about anything. Who's responsible? Depends on the jury.