Members of the Congressional Black Caucus and the Congressional Hispanic Caucus have been at the forefront of the campaign for federal prosecution of George Zimmerman on civil rights or hate crimes charges in the killing of Trayvon Martin.

The lawmakers got the first step toward what they’re after on Sunday, just hours after the former neighborhood watch leader’s acquittal in the Florida criminal case. The Justice Department said it was reopening its inquiry into the February 2012 shooting.

But there is no guarantee the House members — or the 250,000 who have signed a petition on the NAACP web site — will achieve their next goal of a second trial for Zimmerman, or their ultimate objective of seeing him convicted.

“I am disappointed in the jury’s verdict, and heartbroken for the scores of young black men nationwide for whom this verdict delivers a startling message: Our fight for civil rights is far from over,” said Rep. Elijah E. Cummings of Maryland, a senior member of the all-Democratic CBC and the only member who has discussed the shooting death of a close relative. (His teenage nephew was murdered in Norfolk, Va., two years ago.)

“There is still much work to do to ensure that all Americans have equal rights and protection under the law of this country,” Cummings said.

Others who went on television or made statements after the Florida included Chaka Fattah, a CBC member from Philadelphia, and Raúl M. Grijalva, a Hispanic Caucus member from Tucson, Ariz.

All of them were explicit in saying they were not out to prejudge the evidence, but that justice should be as assertive and thorough as possible in pursuing a second criminal indictment against Zimmerman. He is white and the teenager he killed — in self-defense, he maintained — was black.

The criminal section of the Justice Department’s Civil Rights Division, federal prosecutors in Florida and FBI agents together will resume an inquiry paused earlier this year in deference to Florida authorities.

A handful of civil rights and hate crimes statutes might apply to the case. But to win a conviction on any of them, the government would have to convince a jury that Zimmerman’s actions were motivated by racial animosity. Proving that state of mind beyond a reasonable doubt is considered an especially difficult task.

That allegation was not part of the prosecution’s case in the trial that just ended, although Martin’s parents and some civil rights groups say evidence of Zimmerman’s prejudices, and a history as a racial profiler, exist in records of his work as a neighborhood watch leader.

Zimmerman’s lawyers say no such credible evidence exists. They may also be aided by the fact that their client tailed Martin in a gated community, not a public street.