Ordinarily, one's conception of a Boddhisatva indicates a radiant being glowing with compassion. This can be problematic for anyone confronted with a situation in which a bad guy is about to harm some one or many other people and you alone have the ability to stop him. To whom then do you owe compassion, the bad guy, or his victims? Is it possible to act as a Boddhisatva to both?
Hmmm. Looking at the karmic consequences of the bad guy who is about to take a life, it is quite likely that he will spend many reincarnations in one of the hell realms if he is allowed kill another being out of anger or fear, or with any of a variety of criminal intents. An awakened person with a gun, should not hesitate to do the appropriate thing. It has been my experience that most law enforcement and military folks are trained to "stop the threat." In other words, your "intent" in firing your weapon is not necessarily to kill the person presenting a threat, but to stop them. They are about to commit some heinous act that will have devastating karmic results for all involved, and for many people involved in relationship to the victims and the bad guy. If he is allowed to commit this act, karma will ripple through generations.
An awakened mind sees this, and it is with the intent of stopping this promulgation of very bad karma, they act in accordance with their training, to stop the threat.
One of the few teachings I have come across on this topic, I heard on Speaking of Faith, on National Public Radio. Here is the link to Krista Tippitt's interview of Thich Nhat Hanh, in which he mentions the "Fierce Boddhisatva," and subsequent interview of Cheri Maples, a Buddhist Police Officer.
Here is the link: