Mr. Zimmerman, the neighborhood watch volunteer who shot Mr. Martin, was acquitted of all charges by a jury late Saturday.
The federal inquiry, which was started shortly after the shooting last year but had been delayed while the state criminal trial in Florida was under way, was being restarted after civil rights leaders called on the Justice Department to re-examine the case. The leaders said Sunday that they remained convinced that the shooting had a racial element. Mr. Martin, 17, was black.
“There is a pattern of George Zimmerman making dozens of calls to 911 over several years, frequently about young men of color,” Benjamin T. Jealous, the president of the N.A.A.C.P., said in an interview on Sunday. Mr. Zimmerman and his family have defended the shooting as an act of self-defense.
In a statement on Sunday, the Justice Department said that now that the state criminal trial was over, it would continue its examination of the circumstances in the shooting. “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.
The department sets a high bar for such a prosecution. Three former Justice Department officials who once worked in the department’s Civil Rights Division, which is handling the inquiry, said Sunday that the federal government must clear a series of difficult legal hurdles before it could move to indict Mr. Zimmerman.
“It is not enough if it’s just a fight that escalated,” said Samuel Bagenstos, who until 2011 served as the principal deputy assistant attorney general in the division. “The government has to prove beyond reasonable doubt that the defendant acted willfully with a seriously culpable state of mind” to violate Mr. Martin’s civil rights.
Attorney General Eric H. Holder Jr. hinted at those challenges last year.
“We have to prove the highest standard in the law,” Mr. Holder said at a news conference in April 2012. “Something that was reckless, that was negligent, does not meet that standard. We have to show that there was specific intent to do the crime with the requisite state of mind.”
Criminal charges under federal hate crime law have increased significantly during the Obama administration. Between 2009 and 2012, the Justice Department prosecuted 29 percent more such cases than in the previous three fiscal years. Last month in Seattle, for example, Jamie Larson, 49, pleaded guilty to federal hate crime charges that he beat a cabdriver, who was from India and was wearing a turban.
The increase is in part because of the Matthew Shepard and James Byrd Jr. Hate Crimes Prevention Act, enacted in 2009, which removed a requirement that a victim had to be engaged in a federally protected activity, like voting or going to school.
But the Obama administration’s Justice Department has been cautious in its use of the expanded law. In 2010, for example, it turned down calls by civil rights leaders to file charges in New York City in the 2006 death of Sean Bell, a 23-year-old black man who was fatally shot by police officers outside a Queens club just hours before he was to be married.
“There aren’t that many of these cases, and it is not because the government is not being vigilant,” said William R. Yeomans, a former chief of staff in the Justice Department’s Civil Rights Division. “It is very difficult to establish a defendant’s state of mind.”
Hoping this gets through and Zimmerman's the one put on trial this time, not Trayvon.