Trayvon Martin in an undated family photo.  (via AP)

It has been three years since Trayvon Martin, a black 17-year-old, was shot and killed in Sanford, Fla., after an altercation with volunteer neighborhood watch captain George Zimmerman. The complicated case captivated the nation as the public pressure for Zimmerman’s arrest and his subsequent trial — in which he was found not guilty — played out live on cable.

Martin’s shooting, one in a series of high-profile killings of black men and boys by either law enforcement officers or civilians, remains etched in the public consciousness. At a time when a protest movement declaring “Black Lives Matter” has taken to streets in dozens of U.S. cities, the symbols of the Martin shooting — the hoodie Martin was wearing, as well as the Arizona Iced Tea and Skittles that he was carrying — remain commonplace among protest signs.

Zimmerman, who identifies as Hispanic, told police he was fighting for his life and fired at Martin in self-defense. He was acquitted by a Florida jury in July 2013, a decision that prompted demonstrations in cities across the United States.

The case finally, officially, came to a close earlier this week when the Department of Justice announced that it will not seek federal civil rights charges against Zimmerman for the shooting. It was a decision that was widely expected, although it still prompted anger and disappointment from the Martin family and from many civil rights organizations.

[George Zimmerman won’t face civil rights charges in Trayvon Martin’s death]

“He took a life, carelessly and recklessly, and he shouldn’t deserve to have his entire life walking around on the street free. I just believe that he should be held accountable for what he’s done,” Martin’s mother Sybrina Fulton told the Associated Press following the Justice Department’s announcement.

Martin’s parents, Fulton and Tracy Martin, became nationally recognized advocates, and they have worked through the foundation they established in their son’s name to comfort other families who have lost loved ones to gun violence, specifically at the hands of police.

These families form a kind of fraternity as the relatives of black men whose deaths have sparked tough conversations about race and justice: Sean Bell, Oscar Grant, Trayvon Martin, Jordan Davis, Michael Brown, Eric Garner, John Crawford, Tamir Rice.

“Justice demands accountability,” said Sherrilyn Ifill, president of the NAACP Legal Defense and Educational Fund, in a statement following the Justice Department’s announcement that Zimmerman would not face federal charges. “In order for any American to have faith in the criminal justice system, we must have laws that both prevent these kinds of tragedies and ensure that those responsible for senseless deaths, like those of Trayvon Martin, Michael Brown, Eric Garner and countless others, are held accountable for their actions. We must address and eliminate the biases and stereotypes that led to these killings.”

[Turning a moment into a movement after the deaths of unarmed black men]

The deaths in 2014 — Brown, Garner, Crawford and Rice — have propelled new pushes in many statehouses for grand jury and policing reform. Meanwhile, in Washington, there is a new bipartisan momentum for criminal justice reform. On Tuesday, President Obama convened a meeting of 16 lawmakers, Democrats and Republicans, to discuss how to best achieve criminal justice reform this year.

“It was a phenomenal meeting,” Sen. Cory Booker (D-N.J.) said during an interview with Huffington Post Live. He later added: “Getting something done is going to happen . . . there is nothing as powerful as an idea whose time has come.”

Meanwhile, the policy changes that many pushed for in the months following Martin’s death have had mixed success. Advocates for change had hoped that anger about the deaths could be channeled to combat so-called “Stand Your Ground” laws such as the Florida provision that made it unlikely the Martin family could have successfully sued Zimmerman in civil court.

[Was the ‘Stand Your Ground’ law the ’cause’ of Trayvon Martin’s death?]

But, as VICE pointed out earlier Thursday:

Stand Your Ground laws, meanwhile, are still in the books in 22 states. Legislators in at least 13 of those states tried to repeal or limit the statutes in the years since Martin’s death, but only one — Louisiana — was successful. None of the states that were in the process of passing Stand Your Ground laws at the time of the killing have been able to do so.

The advocacy groups born from the anger following Martin’s death did earn a victory earlier this year, when they successfully lobbied lawmakers in Oklahoma to abandon a proposed law that would have outlawed the wearing of hoodies — a proposal that civil rights groups argued would further stigmatize black and brown men and encourage stereotypical fears.