The arrest of George Zimmerman on charges of second-degree murder in the killing of unarmed Florida teenager Trayvon Martin does not mean that justice has been done. But it does provide the opportunity for justice — for a full presentation of the facts before a judge and impartial jury. It was the denial of that opportunity by local officials in Sanford, Fla., who chose not to arrest Mr. Zimmerman immediately after the shooting six weeks ago, that had so inflamed the nation. It led to inevitable questions about whether race was a factor in how the case was handled — Trayvon was black, and Mr. Zimmerman is white and Hispanic — and to outrage at the notion that a young man could be killed without anyone being forced to publicly account for it. Now the Sanford community and the entire nation can get answers about what happened that day, and that is what our criminal justice system is supposed to do.

Angela B. Corey, a special prosecutor brought in from Jacksonville to handle the case, said Wednesday evening that her decision to bring charges was not based on public pressure but on the evidence she had gathered. She declined to say what that evidence is and whether it contradicts in any way the many news reports in the case, but based on what is known so far, her decision to charge Mr. Zimmerman with second-degree murder seems prudent. It is the most serious charge possible for a murder that was not premeditated — as this killing clearly does not appear to be. If convicted, Mr. Zimmerman faces punishment ranging from 25 years to life in prison. But Ms. Corey's decision also preserves the option that the jury could consider lesser charges, such as manslaughter, if that is where the evidence points.

The primary issue in the case is likely to be whether Florida's self-defense law applies in this case. At the urging of the National Rifle Association, Florida lawmakers in 2005 enacted a "stand your ground" law, which eliminates the traditional requirement that a person in fear for his life seek to retreat before using deadly force. Mr. Zimmerman, a volunteer neighborhood watch captain, began following Mr. Martin as the teen walked home from a 7-Eleven where he had bought iced tea and Skittles. Mr. Zimmerman called 911 to report a suspicious person, and despite the operator's instructions, he continued to follow the youth. Mr. Zimmerman's father has said that when the two came face-to-face, Mr. Martin punched Mr. Zimmerman in the nose, knocked him to the ground and began pounding his head into the sidewalk.

Trayvon Martin's side of the story will remain forever unknown. But Ms. Corey can bring to light other crucial details. Did Mr. Zimmerman have any signs of physical injury after the confrontation? What did witnesses see? Where in relation to Mr. Zimmerman was Trayvon Martin when he was shot?

"Stand your ground" is a perversion of the notion of self defense; it makes the use of deadly force the first resort, not the last. And its application in the killing of Trayvon Martin is a perversion even of "stand your ground." The law cannot give impunity to a person who initiates a confrontation and carries it to its ultimate conclusion. It cannot be a justification for wanton vigilantism.

But that is what has happened in Florida, where findings of justifiable homicide have skyrocketed since "stand your ground" went into effect. New York Mayor Michael Bloomberg this week launched a national campaign to repeal "stand your ground" laws, versions of which have been enacted in 25 states (Maryland, thankfully, not among them). He is right that the laws contribute to a "shoot first, ask questions later" culture that makes society less safe, not more.

There can be no question that Sanford was made less safe by George Zimmerman's actions. Trayvon Martin and his family can get justice in the courtroom through a determination of whether Mr. Zimmerman's reckless and foolish conduct was criminal. But the state of Florida and the nation can only restore the balance of justice by repealing these reckless and foolish laws.