Mayor Michael Bloomberg backed a national effort to overturn so-called "stand your ground" laws Wednesday, saying the law at the heart of the Trayvon Martin case promotes vigilantism. 

The mayor was in Washington, D.C., to announce a national campaign to overturn the laws, which exist in 25 states.

"These laws have undermined the integrity of the justice system and done real harm to public safety," Bloomberg said.

Bloomberg said many states that've passed such laws have seen an increase in so-called justifiable homicides. He noted in Florida, the average number of those cases rose from 12 to 36, after the law was passed.

"These shoot-first laws have nothing to do with that, or with the exercise of second amendment rights," Bloomberg said. "Instead, they justify civilian gunplay and invite vigilante justice and retribution with disastrous results."

A call placed to the NRA for comment was not returned.

Trayvon Martin, an unarmed, black teenager, was shot dead in February at the hands of a neighborhood watch volunteer who says he was acting in self-defense.

Bloomberg said George Zimmerman, who had previous arrests for assaulting a police officer and domestic violence, never should have had a gun in the first place.

Separately, a law enforcement official says that charges are being filed in the shooting death of Martin later Wednesday.

Annmarie Fertoli and the Associated Press contributed reporting.