Last weekend's acquittal of George Zimmerman in the shooting death of Trayvon Martin in Sanford, Fla., calls to mind Minnesota's debate over its self-defense statute and how it should be applied — especially when 114,793 private citizens have permits to carry weapons in public.

Last year, when the GOP was in the majority but often faced a roadblock in DFL Gov. Mark Dayton, the Legislature passed a bill authorizing the "use of deadly force in defense of home and person." It was backed by the National Rifle Association and state gun-rights groups and opposed by law enforcement. Dayton vetoed it. Supporters called it "Stand your ground" and opponents called it "Shoot first."

Florida has such a law, sometimes called an "expanded castle doctrine" because it extends the law for defending one's "castle" out into public places. The Florida law expands the legal justification for self-defense and was cited as the reason Zimmerman, who had a permit to carry his weapon, was not initially charged. After an uproar, a second prosecutor filed second-degree murder charges, and the judge's jury instructions appeared to track the "stand your ground" theory of self-defense.

In Minnesota, "justifiable taking of life" by a civilian is defined as "when necessary in resisting or preventing an offense which the actor reasonably believes exposes the actor or another to great bodily harm or death, or preventing the commission of a felony in the actor's place of abode."

Prosecutors say this allows for legitimate self-defense, and gives the "actor" — the person firing the shot — considerably more latitude to act in self-defense against a home intruder. In killings outside the home, courts can take into account whether the actor tried to get away from the confrontation, a concept known as the "duty to retreat."

The law Dayton vetoed would have replaced the "justifiable taking of life" language with a longer and more complicated self-defense standard. The two sponsors, Rep. Tony Cornish, R-Vernon Center, and former Sen. Gretchen Hoffman, R-Vergas, are gun-rights activists who often carried their weapons at the Capitol. The law would have expanded the "castle" self-defense law to a person's car, tent or boat; it would have done away with the duty to retreat as a mitigating factor; and it would have expanded the legal definition of self-defense and justifiable killings that prosecutors, judges and juries must follow.

Laws matter after the fact, when a deed has been done and a case comes to trial. But they also set the standard for acceptable behavior. In 2012, the Minnesota Law Enforcement Coalition worried that "stand your ground" laws justify "escalating the level of violence."

"Such a law would, in essence, allow persons to shoot first and ask questions later whenever they believe they are exposed to substantial harm, regardless of how a reasonable person would have responded under the circumstances or perceived the gravity of the danger faced," said the group, representing police officers, chiefs, prosecutors and sheriffs. "Substantial bodily harm includes a chipped tooth or a broken nose. Someone receiving these injuries in a fight could retaliate by killing their opponent."

In light of the head wounds Zimmerman suffered in the struggle with Martin, the phrase sounds prescient.

Meanwhile, the "castle doctrine" lives in Minnesota, but has its limits. In Little Falls, a 64-year-old man has been charged with second-degree murder for killing two teenagers who were burglarizing his home, allegedly firing multiple times.

People would agree that a decision to shoot is a grievous, irreversible act. Having decided to allow gun-carrying, Minnesota and other states surely will be pressed to define more clearly when a gun may be used. If the Zimmerman-Martin case shows anything, it is that such cases are often not clear-cut examples of the "good guys" vs. "bad guys" narrative, but real-life tragedies shrouded in moral ambiguities.