You are going to be arrested if you shoot somebody, even if the guy is toting a machine gun. No matter what you say, you will be arrested. So, you tell the police that you intend to cooperate but won't discuss what happened until you've spoken to your attorney. Your attorney helps you craft a statement which satisfies the police/DA's needs but which doesn't give the perp's attorney anything to use against you.
That all depends on what state you reside in.
Not in Texas thank God.