Federal prosecutors concluded there is not sufficient evidence to prove Zimmerman, a neighborhood watchman in Sanford, Fla., intentionally violated Martin's civil rights.
"Although the department has determined that this matter cannot be prosecuted federally, it is important to remember that this incident resulted in the tragic loss of a teenager's life," Acting Assistant Attorney General Vanita Gupta of the Civil Rights Division said. "Our decision not to pursue federal charges does not condone the shooting that resulted in the death of Trayvon Martin and is based solely on the high legal standard applicable to these cases." The case sparked intense discussions over race in America because Martin was walking to his home with only Skittles and an iced tea in his hands.
One juror -– the only minority on the all-female jury –- later told ABC News that "as the law was read to me, if you have no proof that he killed him intentionally, you can't say he's guilty."
"You can't put the man in jail even though in our hearts we felt he was guilty," she said. "But we had to grab our hearts and put it aside and look at the evidence."
In Sanford, race-related tensions had been simmering for nearly a century, but Martin's death "was the proverbial 'straw that broke the camel's back,'" bringing "those issues to the surface," the new Sanford police chief, Cecil Smith, recently told federal officials.
After Martin was killed, Holder sat down his own teenage son to explain that -- as unfair as it may be -- young black men must often interact with police in a different way than others, he told a convention in April 2014. It was "a conversation I hoped I'd never have to have," Holder added.
Zimmerman was not a police officer and the neighborhood watch program he was a part of was independent from local police.
Many accused Zimmerman of discriminating against Martin –- essentially taking action against the teenager and ultimately killing him because Martin was black. Zimmerman is Hispanic.
Privately and publicly, Justice Department officials have been telegraphing all along that they were unlikely to file charges against Zimmerman. And in November 2013, Holder said the case against Zimmerman "in substantial part was resolved" with his acquittal months earlier.
Nevertheless, federal officials have insisted their civil-rights probe would be thorough and complete. Several months ago –- nearly two years into the Justice Department's investigation –- Holder said federal investigators were still seeking to interview certain witnesses "as a result of some recent developments."
More recently, Holder has said he hoped to announce the findings of the Zimmerman and Ferguson-related probes before he leaves office, which could happen in a matter of weeks, depending on when the U.S. Senate confirms his successor.
Holder has said then when a decision is announced in the Zimmerman case, it will be accompanied by "as much information" as possible detailing the Justice Department's findings.
In the Ferguson case, the department is currently conducting two probes into the matter.
A criminal investigation will try to determine whether then-officer Darren Wilson used unreasonable force and intentionally violated Michael Brown's civil rights when he shot the unarmed teenager in August. The second probe - though not criminal in nature –- will look more broadly into whether the Ferguson police department has routinely engaged in a "pattern or practice" of unlawful and discriminatory policing.
A state grand jury in Ferguson, Missouri, declined to indict Wilson in Novembe4 2014. Many expect the Justice Department will not be able to bring federal charges against Wilson, but will take action against the local police department.