The department opened an investigation into Martin's death last year but stepped aside to allow the state prosecution to proceed.
In a statement, the Justice Department said the criminal section of its civil rights division, the FBI and the U.S. Attorney's office for the Middle District of Florida are continuing to evaluate the evidence generated during the federal probe, in addition to the evidence and testimony from the state trial.
"Experienced federal prosecutors will determine whether the evidence reveals a prosecutable violation of any of the limited federal criminal civil rights statutes within our jurisdiction," the statement said. Justice added that it will determine "whether federal prosecution is appropriate in accordance with the department's policy governing successive federal prosecution following a state trial."
From the Rodney King case in Los Angeles to the Algiers Motel incident in Detroit more than four decades ago, the Justice Department has a long history of using federal civil rights law in an effort to convict defendants who have previously been acquitted in related state cases.
On Sunday, NAACP President Benjamin Todd Jealous started a petition calling for the Justice Department to open a civil rights case against Zimmerman for the shooting death of 17-year-old Martin, but experience has shown it's almost never easy getting convictions in such high-profile prosecutions.
"The Justice Department would face significant challenges in bringing a federal civil rights case against Mr. Zimmerman," said Alan Vinegrad, the former U.S. Attorney in the Eastern District of New York. "There are several factual and legal hurdles that federal prosecutors would have to overcome: They'd have to show not only that the attack was unjustified, but that Mr. Zimmerman attacked Mr. Martin because of his race and because he was using a public facility, the street."
As to the last element, the confrontation between Zimmerman and the shooting victim occurred in a gated community, which may not fit the legal definition of a public facility.
Lauren Resnick, a former federal prosecutor in New York who successfully prosecuted a man in the killing of an Orthodox Jew during the 1991 Crown Heights riots in Brooklyn, said the Justice Department could conceivably proceed under a theory that Zimmerman interfered with Martin's right to walk down a public street based on his race. But that would be challenging, she said, because it would require prosecutors to prove, among other things, that trailing Martin on the street constituted interference.
"One could argue it did, if it freaked him out and he couldn't comfortably walk down the street - there's an argument here," said Resnick, who now specializes in white-collar criminal defense and commercial litigation.
But she said federal prosecutors were likely to encounter the same hurdles as state prosecutors in establishing that Zimmerman was driven by racial animus and was the initial aggressor, as opposed to someone who acted in self-defense.
"When you have a fact pattern where one person's alive, and one person's not, and the person alive is the defendant, it's hard to prove things beyond a reasonable doubt," said Resnick. She also said it was easier to prove a criminal bias in the Crown Heights killing than it would be in any federal prosecution of Zimmerman.
Samuel Bagenstos, a former No. 2 official in the Justice Department's civil rights division, said: "This is an administration that hasn't shied away from bringing hate crimes cases that are solid prosecutions based on the facts and the law, but from what I've seen this would be a very difficult case to prosecute federally because the government would have to prove beyond a reasonable doubt that George Zimmerman acted because of Trayvon Martin's race. If you're trying to prove racial motivation, you are usually looking for multiple statements related to why he is engaging in this act of violence. I think it's a difficult case to prove."
Another federal case, the Rodney King prosecution, illustrates just how difficult it can be for the federal government to come in behind a state prosecution that ended in acquittal, even when there's videotaped evidence of the crime.
King was beaten by Los Angeles Police Department officers after a high-speed car chase in 1991, but the four police officers charged in the incident were acquitted on state charges of assault with a deadly weapon and three of the four were acquitted on a charge of use of excessive force. The jury deadlocked on the excessive force charge against the fourth officer.
Federal prosecutors obtained an indictment on charges of violating King's civil rights. Two of the officers were found guilty and were imprisoned. The other two officers were acquitted.
In a 1970 prosecution, the Justice Department charged three white Detroit police officers and one black private security guard with allegedly conspiring to deprive eight black youths and two white girls of their civil rights during the 1967 riots in Detroit.
The officers had gone to the Algiers Motel in a reported search for snipers. Three black teenagers were slain at the motel. One of the police officers had been acquitted earlier of a state charge of first-degree murder in the case; another officer had been found innocent in a separate state trial on a charge of felonious assault.
The federal case took place in Flint, Mich., an hour's drive north of Detroit, after the defense complained that the defendants could not get a fair trial in the city where the slayings occurred. A jury acquitted all four defendants.
In prosecuting the law enforcement officers, the Justice Department invoked an 1871 civil rights law. Prosecutors alleged that the officers had lined up the people staying at the motel and slugged them with clubs and rifle butts. There was testimony that several of the guests were taken into separate rooms where shotguns were fired into the ceiling in an effort to get those in a nearby hallway to disclose the identity of the alleged snipers and the location of firearms.
In a defense that turned out to be successful, defense attorneys emphasized that the charge against their clients was conspiracy, not assault, coercion, intimidation or murder. Lawyers for the two officers previously charged in the state cases also argued that their clients were being charged with serious criminality even though they had already been acquitted.