...First, IANAL. New Mexico has a Castle Doctrine, but, as interpreted by the courts, it's pretty weak. The simple fact that someone has broken into your house or is in the act of stealing your goods is probably not enough to justify the use of deadly force, as interpreted by the NM courts. Deadly force in the case of a clear cut threat to your life or the lives of your loved ones (BG has gun/has fired gun) will PROBABLY be ruled justifiable homicide. In between, is where it gets tricky. A 5', 90 lb. woman threatened by an unarmed 6' 3", 275 lb man -- deadly force probably justified. A 6', 210 lb. man threatened by same unarmed BG -- deadly force perhaps not justified/perhaps so.
Think before you act and, should you be involved in the use of deadly force, take some time to think before talking to the authorities -- tell them you'll cooperate, but you're very shaken and need some time to settle down. This is one big gray area and the picture you paint will have a BIG influence on how your situation is viewed. So, think before you act and think after you act.