By John R. Lott Jr.

On Sunday, Mayor Michael Bloomberg knew what was responsible for Trayvon Martin's death: Florida's "Stand Your Ground" law. Or, as Bloomberg calls it: a "shoot-first" law.

According to Bloomberg: "'shoot-first' laws like those in Florida can inspire dangerous vigilantism and protect those who act recklessly with guns. Such laws - drafted by gun-lobby extremists in Washington - encourage deadly confrontations by enabling people to shoot first and argue 'justifiable homicide' later."

Many others have taken the same line since Saturday's verdict. But they don't understand the law. Nor do they understand why it was completely irrelevant to the George Zimmerman trial. But on Tuesday night, Attorney General Eric Holder renewed his call for these laws in Pennsylvania and more than 30 other states to be overturned.

Prior to "Stand Your Ground," citizens had to retreat as far as possible and then announce to the criminal that they were going to shoot. The "Stand Your Ground" law drops the original requirement to retreat. But lethal force is still only justified when a reasonable person would believe that a criminal intends to inflict serious bodily harm or death. The law doesn't protect anyone who provokes a confrontation.

Apparently forgotten is the reason that "Stand Your Ground" laws exist. Delays in letting people defend themselves sometimes prevented people from defending themselves. Trying to define an "appropriate retreat" adds confusion. Prosecutors have sometimes abusively claimed that people who defended themselves could have even retreated farther than they did.

Zimmerman's defense never raised the "Stand Your Ground" law. Obviously, if Zimmerman was on his back and Martin holding him down, Zimmerman had no option to retreat. So the law was completely irrelevant, but you would never know that from the discussion this week.

Much was made by the prosecution of a criminal justice course that Zimmerman took at Seminole State College. If Zimmerman remembered that class, then he knew the law. He would have known it did not give him a license to "shoot first" and ask questions later.

If we are to talk about Florida, it is hard to ignore how law-abiding concealed-handgun permit holders are. From January 2008 to June 2013, only four additional Floridians have had their permit revoked for any firearms-related violation. With more than one million active permit holders, that is an annual revocation rate of a minuscule 0.00007 percent. (One other important point about Florida: African Americans have used "Stand Your Ground" laws at a much higher rate than whites.)

Indeed, in state after state, permit holders lose their permits at hundredths or thousands of 1 percent for any type of gun-related violations.

Police in the United States are extremely sympathetic with concealed-handgun laws. For example, consider a March survey of active-duty and retired police by PoliceOne, an organization with more than 400,000 police officers as members. It found that out of the 14,200 members who answered their survey, 91 percent supported concealed-handgun permits "without question and without further restrictions."

A National Association of Chiefs of Police 2010 survey found 77 percent believe that civilians permitted concealed handguns "facilitate the violent-crime-fighting potential of the professional law enforcement community."

One final number that is hard to ignore: The U.S. murder rate fell 15 percent between 2007 and 2012, but at the same time the number of concealed-handgun permits doubled from 4.5 to more than 9.3 million. The beneficial impact of concealed carry is further confirmed by the vast majority of peer-reviewed academic research by economists and criminologists.

My own research shows that law-abiding poor blacks who live in high-crime urban areas benefit the most from having concealed handguns for protection.

Critics of gun ownership might not want to admit it. But police can't be everywhere, and sometimes people, such as George Zimmerman, need to defend themselves.