Attorney General Eric Holder Jr. is in the middle of a political and legal balancing act following the acquittal of George Zimmerman in a racially-charged murder case, with civil rights leaders calling on U.S. Department of Justice to take legal action and federal laws that might not make that possible.

In his first comments since Saturday’s not-guilty verdict and subsequent protests around the country, Holder told the Delta Sigma Theta sorority in Washington on Monday that civil rights leaders are right to be concerned about the “unnecessary” shooting death of Trayvon Martin in Sanford, Fla., last year.

“I believe that this tragedy provides yet another opportunity for our nation to speak honestly about the complicated and emotionally-charged issues that this case has raised,” said Holder, who was introduced as the first black attorney general. “We must not – as we have too often in the past – let this opportunity pass.”

But Holder, while acknowledging his department’s open investigation of the Zimmerman case, avoided commenting on demands from civil rights leaders such as the National Association for the Advancement of Colored People that federal prosecutors file civil rights charges against Zimmerman.

“I want to assure you that the Department will continue to act in a manner that is consistent with the facts and the law,” Holder said during a previously scheduled speech.

On Tuesday, Holder is scheduled to address the NAACP directly with a keynote address during the group’s annual convention in Orlando, close to where the Zimmerman trial took place. The group’s website demands action by the Justice Department and asks visitors to sign a petition.

“We ask that the Department of Justice file civil rights charges against Mr. Zimmerman for this egregious violation. Please address the travesties of the tragic death of Trayvon Martin by acting today,” the petition reads.

The American Civil Liberties Union also asked the Justice Department to continue an investigation and determine whether there was a federal civil rights violation or hate crime, and called for other changes that would clarify the muddy area of racially motivated crimes.

“We call on Attorney General Eric Holder to release strengthened guidance on the use of race in federal law enforcement,” ACLU executive director Anthony Romero said. “We also urge Congress to pass the End Racial Profiling Act. These specific actions would go a long way to ameliorate the widespread problem of racial profiling.”

The case sparked a national debate over racial profiling and self-defense, particularly after President Barack Obama addressed the killing of the 17-year-old during the presidential election. Martin was shot while walking through the gated townhouse community where he was staying and where Zimmerman lived, according to Associated Press reports on the three-week trial. None of the witnesses who were called had a clear view of their encounter.

Defense attorneys said the case represented classic self-defense, claiming Martin knocked Zimmerman down and was slamming his head against the concrete sidewalk when Zimmerman fired his gun.

Now that the trial is over, Justice Department lawyers will start reviewing the evidence to determine whether federal charges are appropriate. “It’s important for the department to do a vigorous investigation, and who knows what will come out,” said William Yeomans, a former acting assistant attorney general now a professor at American University Washington College of Law. “There may be holes that can be filled in once the FBI joins in.”

Yeomans and other former government prosecutors said Tuesday that federal charges are possible under the new Matthew Shepard hate crimes law, but that the Justice Department would have several difficult hurdles to overcome, especially considering the evidence that has come out so far in the case.

“The big hurdle is establishing the defendant’s state of mind and showing he acted with racial motivation,” Yeomans said. “It’s not impossible,” but “the evidence developed so far would make that difficult.”

While many of the facts suggest Zimmerman, 29, had racial motivations for confronting Martin, prosecutors would have to show willful racial intent—that “at the time he inflicted bodily harm, he was thinking of race,” Yeomans said.

Lauren Resnick, a former federal prosecutor with BakerHostetler’s white-collar defense practice in New York, agreed that proving that racial element would be the key.

“The federal investigation will hinge on the quality of evidence to show that Zimmerman had a racial motive for singling out and following Martin in the first place and that he was not acting in self-defense when he fired his gun,” Resnick said. “To prevail at a federal trial, the prosecutors would need to establish both of those facts beyond a reasonable doubt.”

Yeomans said the successful cases, generally, have involved defendants who made contemporaneous statement of racial animus, had a history of racially motivated acts or statements, or had earlier conversations with co-conspirators about their motivation. None of that appears present in the Zimmerman case right now.

“Without that kind of evidence, it’s very difficult,” Yeomans said.

President Barack Obama, in a statement issued Sunday, called Martin’s death a tragedy “not just for his family, or for any one community, but for America.” Obama said the way Americans can honor Martin is through self-reflection.

“And as we do, we should ask ourselves if we’re doing all we can to widen the circle of compassion and understanding in our own communities,” Obama said. “We should ask ourselves if we’re doing all we can to stem the tide of gun violence that claims too many lives across this country on a daily basis. We should ask ourselves, as individuals and as a society, how we can prevent future tragedies like this.”

Contact Todd Ruger at truger@alm.com.