They are joining the Trayvon Martin crusade by the hour now.

It feels like an echo from another era — when there was racial injustice in the headlines, when federal troops were dispatched to comb Southern swamps to look for blacks who had vanished.

And when lawyers for the NAACP slid into town with briefcases and addresses of safe houses.

It feels like the not-so-long-ago ’60s, back when getting federal authorities to move quickly was often difficult. But this is a different era, however tragically similar the outcome.

The Trayvon Martin story has multiple layers: a black victim, a Hispanic man who did the shooting in Sanford, Fla. In Washington, the head of the Justice Department’s civil rights division, Thomas E. Perez, is Hispanic. The attorney general of the United States, Eric H. Holder Jr., is a black man. The man who occupies the Oval Office, Barack Obama, is an African American.

And yet, even that arc of progress — while admired — hasn’t softened emotions and feelings.

“It reminds you of Emmett Till,” said Bernadette Pruitt, an associate professor of history at Sam Houston State University in Huntsville, Tex., who has written about Southern racial history and can’t stop thinking of Trayvon Martin and his family. “This so-called post-racialism is a figment of our imagination. Race, unfortunately, is still the barometer by which everyone is measured.”

Investigating the killing of the 17-year-old Martin, who was black, by neighborhood watch captain George Zimmerman, who is Hispanic, is now a top priority for the FBI, senior law enforcement officials said Wednesday.

One focus of the FBI’s inquiry is whether Zimmerman muttered a racial slur seconds before shooting Martin on Feb. 26, as has been alleged. The FBI is trying to determine whether the audiotape of a 911 dispatch call between Sanford police and Zimmerman can be enhanced with sophisticated equipment that has been used in other cases. If it can, the tape will be transferred to the FBI laboratory at Quantico, one official said.

Enhancing the tape could be crucial to determining whether the shooting is considered a “hate crime” under federal hate-crime laws, according to law enforcement officials.

Top Justice officials were scheduled to meet Thursday in Florida with the Martin family and the family’s attorney. And Holder on Friday is scheduled to meet with black ministers at the White House, where the Martin case is expected to come up, according to a government official.

On Wednesday in Sanford, the doors of a black church swung open so those in pain could sit, or stand, and give vent to their hurt. Benjamin Jealous, NAACP president, was in town. He was there to deal with the death of an unarmed teenager on a darkening street. Zimmerman has claimed self-defense. The mourners showed up at Olive Street Baptist Church to pray for justice and talk about their run-ins with Southern law enforcement. Anger seemed to outweigh prayer.

One after another, they filed to the front of the red-carpeted sanctuary to tell their stories.

Mary Scott said her son was shot to death by police in 2010, a killing that she said was unjustified and remains largely uninvestigated. “I’ve got animosity in my heart,” she said.

Lula King, 75, said her grandson was brutally beaten by three correctional officers after he had a seizure while in custody: black eyes, cuts and a “knot on his head bigger than a hen egg.” The men who beat him, wrongfully she said, had never faced discipline.

They were hanging on her every word.

She continued: “But I’ll tell you, God is gonna take care of all of this,” she said to shouts of “Amen!” from the crowd. “Whatever men do wrong, it’s gonna come to the light.”

The stories kept coming, as if it were hoped that they would provide some kind of salve for those who knew and loved Trayvon. People were testifying, a ritual in the black church. The facts about each case were impossible to parse on the spot, and possibly lost forever. But the sentiment behind the stories was unmistakable: Bad things had been done to others with the same promise as Martin. Too many questions had gone unanswered.

Martin has been swooped up this quickly, linked with names from the annals of history. “We can name names all the way from Emmett Till to Trayvon Martin,” said Hannibal Duncan, 32, who told about black friends who had been profiled repeatedly and, in one case, beaten by police. “At some point, we’ve got to find some kind of way to stop it.”

On this same day, Sanford City Manager Norton Bonaparte Jr. posted online a letter addressed to “Fellow Citizens” that tried to answer some of the public’s vexing questions.

Why did Zimmerman have a firearm in his role as neighborhood watchman? He was authorized to carry a concealed weapon, according to Bonaparte.

Why wasn’t Zimmerman arrested the night of the shooting? “By Florida statute, law enforcement was PROHIBITED from making an arrest based on the facts and circumstances they had at the time,” Bonaparte wrote.

By Wednesday evening, the Sanford City Commission had taken a vote of “no confidence” in the police chief.

Zimmerman’s family has said he is not a racist and that he has black friends to prove it. Zimmerman, 28, who grew up in Manassas, in Northern Virginia, has gone into seclusion. But others are speaking up for him. One of them is Frank Taaffe. Taaffe, 55, moved to Zimmerman’s Sanford neighborhood in 2006.

He said it has changed drastically in the years since the housing crisis hit. Prices have fallen. Renters have replaced owners. Neighbors don’t know one another as well as they used to. A rash of burglaries had put everyone on edge in the months before Martin was shot.

“We had the perfect storm,” Taaffe said. “Everybody was on high alert.”

Taaffe said he certainly doesn’t condone Martin’s shooting, but he insisted that the demonization of Zimmerman is its own tragedy. He said Zimmerman had helped to prevent burglaries and looked out for his neighbors as much as anyone.

“George is a good dude. He’s a good guy. He cares about this community. He’s not a vigilante out looking for trouble. . . . He’s not a Bernhard Goetz,” Taaffe said, referring to the New York “subway vigilante” of the 1980s. “He’s more like Mr. Peepers.”

Taaffe said that if Zimmerman deserves punishment, it should come through the legal system rather than in the court of public opinion. But the court of public opinion is roiling. The Martin saga has generated discussion from hair salons to the halls of academia, and it has exploded on social media.

What started as a local news story went national after the news services picked it up, and such influential bloggers as the Atlantic’s Ta-Nehisi Coates and the Huffington Post’s Trymaine Lee called attention to it early on. Much as with the Kony 2012 campaign, celebrities quickly jumped into the online fray, and the Martin case picked up steam. Hip-hop mogul Russell Simmons may have been the first celebrity to notice the story, sharing a Facebook page in mid-March with thousands of Twitter followers to demand justice for Martin.

“Trayvon Martin didn’t die so we can create a race war. He died so we can promote better understanding,” Simmons wrote.

Mia Farrow soon followed suit, telling her followers about the case and using the hashtag #Justice4Trayvon. Within days, that hashtag and others related to the killing started trending.

After a petition demanding justice for Martin languished for weeks, filmmaker Spike Lee’s retweet of a link for the petition caused it to take off. Now, calls the petition demanding Zimmerman’s arrest the fastest-growing petition in Internet history. It has more than 900,000 signatures. Radio talk show host Michael Baisden and activist Al Sharpton were among the others who had a hand in galvanizing public interest.

By Wednesday evening, hundreds wearing hooded sweatshirts were marching in New York City in memory of Martin, a demonstration labeled “the Million Hoodie March.” In his call to police, Zimmerman said that the “suspicious” person he saw, who turned out to be Martin, was wearing a hoodie.

Pruitt, the associate history professor, said the nation’s shock and the attention to the saga can be explained in the simplest terms: “People are caught off guard. They’re going ‘Wow. This is a kid. From the neighborhood. He wasn’t committing a robbery or anything.’ ”

He liked Skittles, which he had just bought from a local store, along with iced tea. He had a girlfriend. And his dream has been ended.

“There is the brutal nature of this,” said former Washington Post reporter Nathan McCall, a lecturer at Emory University who served time in prison himself and has spoken often about young black men and the criminal justice system. (Martin did not have a criminal record; he earned A’s and B’s in school.) “This sounds like a narrative out of the 1950s, where yet another black man gets randomly killed and the institutions in society that are supposed to respond, don’t respond accordingly. They blame the victim.”

The killing is likely to keep the soul-searching discussions around the country going for a while, particularly among blacks. Talks about race, the vulnerability of young black males, small-town justice and gun laws.

This is what happened two generations ago in Money, Miss. It was Aug. 24, 1955. A 14-year-old kid, visiting the state on vacation from Chicago, walked into a country store. He saw a white woman, Carolyn Bryant, and supposedly whistled at her. When her husband, Roy Bryant, and his half-brother, J.W. Milam, heard about it, they vowed revenge.

And a few days later they rousted Till from sleep, drove the terrified boy around the dark Delta, shot him in the back of the head and dropped him into a river.

His killers, tried by an all-white jury, were acquitted amid cackling in the courtroom.

Mamie Till, the child’s mother, insisted her son’s casket be open. And so, it seems, began a good part of the modern civil rights movement. Hundreds lined up around the Chicago church where the funeral took place, the picture of Emmett in his casket publicized for all the world to see in Jet magazine.

“We forget about Southerners,” Pruitt said. “We so often associate black progress with a movement of African Americans out of the South. It isn’t shocking to me that the people in Florida said, ‘We’ve got to do something.’ ”

Haygood and Horwitz reported from Washington. Dennis reported from Sanford. Elizabeth Flock contributed to this report from Washington.