U.S. Attorney General Eric Holder says the Justice Department will take action in the case of an African-American teenager killed in Florida, if it finds evidence that a federal criminal civil rights crime was committed.

Holder spoke Wednesday at the annual convention of the National Action Network, a civil rights organization founded by African-American civil rights leader the Reverend Al Sharpton.

Holder said the Justice Department will conduct a thorough and independent review of the Trayvon Martin case, calling it a “tragedy that we're struggling to understand.”

“Although I cannot share where current efforts will lead us from here, I can assure you that, in this investigation – and in all cases – we will examine the facts and the law. If we find evidence of a potential federal criminal civil rights crime, we will take appropriate action. And at every step, the facts and the law will guide us forward.”

The 17-year-old Martin was shot and killed last month by a white Hispanic man who led a neighborhood watch program.

George Zimmerman told police he acted in self-defense when Martin attacked him. But Martin's family says the young man was unarmed and confronted because of his race. They are demanding Zimmerman be charged with murder.

A recording of an emergency telephone call to police during Martin's and Zimmerman's confrontation is inconclusive.

The case has ignited a debate about racial tensions in the United States. Martin supporters say the shooting shows how young black men are constantly threatened with violence, while Zimmerman supporters say race had nothing to do with the killing.

On Tuesday, Zimmerman's lawyers pulled out of the Florida case, saying they had lost contact with their client, despite repeated efforts to reach him.

Attorneys Hal Uhrig and Craig Sonner said they can no longer represent a client who will not communicate with them. But they said they are concerned for Zimmerman's safety, saying he has “a bounty” on his head.

Late Tuesday, special prosecutor Angela Corey announced she will hold a news conference later this week to disclose new information in the case. It is up to Corey to decide whether to prosecute Zimmerman.