If it is possible, ask another person to call the police. Why is this important? It is better to have someone who is not in a shock to call the police; it would be better not to have a voice recording while you are in a stressful moment. The dispatch operators will keep you on the phone a little longer, so they can get as much information as possible.
Later, the tape will be played in your case. It is a good way not to give the prosecutor a chance to use it against you.
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If there are witnesses, don’t tell them what happened. People will ask you a million questions, but make sure you don’t talk. You are still in shock. Keep in mind that every witness will be asked to testify. Whatever happens, after you shoot, becomes a piece of evidence – your words, your behavior, people you spoke to, everything.
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So it happened – now get yourself together and do not touch anything. The law is not requiring you to give medical aid to your attacker. You can face penalties for tampering with the crime scene. Sure, it would be odd to get away from the scene, but it is the best thing to do.