The most infamous 1960s Deep South civil rights murders have inspired a steady stream of books over the past 50 years. The three best-known killings — the June 1963 assassination of Mississippi NAACP leader Medgar Evers; the September 1963 bombing of the Sixteenth Street Baptist Church in Birmingham, Ala., which killed four young girls; and the June 1964 murders of civil rights workers Michael Schwerner, James Chaney and Andrew Goodman in Neshoba County, Miss. — have all become staples of American historical memory.

In 1988, the somewhat fictionalized movie “Mississippi Burning” elevated the Neshoba killings to widespread fame, portraying FBI investigators as the heroes of the black freedom struggle. Two decades earlier some of the killers, including the Mississippi Klan’s imperial wizard, Samuel Bowers, served modest prison terms based on federal civil rights charges, but other top conspirators, including Edgar Ray Killen, walked free. Likewise, in Birmingham, well-known Klansman Robert “Dynamite Bob” Chambliss was sent to prison in the late 1970s, but his three fellow bombers eluded prosecution. Evers’s well-known killer, Byron De La Beckwith, remained a free man after two Mississippi juries deadlocked on the charges against him.

When “Mississippi Burning” was first screened in Jackson, Miss., one viewer was 29-year-old Clarion-Ledger reporter Jerry Mitchell, who had joined the state’s premier newspaper three years earlier. Two others were retired FBI officials who had overseen Mississippi in the 1960s, and from follow-up conversations with them, Mitchell gradually realized just how many widely suspected Klan killers had never been convicted of murder. For the next quarter-century, Mitchell would devote much of his time and energy to reporting on how those cold cases could be reopened and prosecuted.

In his book, “Race Against Time,” Mitchell describes how, by the 1990s, suspects and witnesses were increasingly dying off. The easiest case to revive was that against Beckwith: His mistrials did not preclude yet another attempt to convict him of Evers’s murder, and in early 1994 a new jury did just that. One new witness against Beckwith was his nephew, Reed Massengill, who had just published an invaluable book about his uncle appropriately titled “Portrait of a Racist.” Evers’s and Beckwith’s lives have been so well-chronicled that “Race Against Time” covers largely familiar ground, but Mitchell does highlight how a Klan buddy whom Beckwith once called “his guiding force,” Gordon Lackey, was equally complicit in Evers’s murder. “We drew, and I ended up with the short straw,” Beckwith admitted shortly after his conviction. Lackey, however, was never charged; he died in 2007.

In time, two of the three remaining Birmingham church bombers, Tommy Blanton and Bobby Cherry, would also be convicted in the four girls’ murders; the fourth, Herman Cash, died in 1994. A crucial piece of evidence against Blanton came from an FBI microphone bug surreptitiously implanted in the wall of Blanton’s home, which heard him telling his wife, “We had that meeting to make the bomb.”

Mitchell’s valuable memoir again and again illuminates both the seedy worlds of hate-filled Klansmen and the wide-ranging tactics that lawmen used in pursuing them. Top Neshoba suspect Killen had little hesitation in speaking with Mitchell on multiple occasions. When Mitchell in 2002 asked Killen about the killers of the three civil rights workers, he forthrightly replied, “I’m not going to say they were wrong,” because the young victims were communist agents, he insisted. “I don’t believe in murder. I believe in self-defense,” Killen explained. Only in 2005, 16 years after Mitchell first saw “Mississippi Burning,” was Killen finally convicted in the three killings.

Along the way, Mitchell learned that both of his next-door neighbors in suburban Jackson had ties to the Neshoba County killers. One morning one of the men informed Mitchell that he had recently visited there and learned that “the Klan wants to kill you.” The neighbor jokingly added that “I told ’em if they wanted to know where you lived it would cost them big bucks,” but Mitchell found no humor in the remark.

The book’s most important scoop also involves money, namely the $30,000 in cash — almost $250,000 in today’s dollars — that was delivered to FBI inspector Joe Sullivan for payment to a secret informant who would reveal where the Neshoba Klansmen had buried the three civil rights workers’ bodies. Mitchell’s indefatigable reporting leads him to identify Mississippi Highway Patrolman Maynard King, who died in 1966, as Sullivan’s informant, but King’s family convinced Mitchell that he never received any such money. Mitchell weakly theorizes that Sullivan must have used the huge sum for other incidental expenses and avoids confronting the possibility that the famed lawman, who died in 2002, may have pocketed much if not all of that cash.

Only at the very end of “Race Against Time” does Mitchell confess that the successful prosecutions his memoir highlights represent only a minority of the civil-rights-era killings he investigated, and that far more “cold cases ended with no convictions” or indictments. “I failed far more often than I succeeded in the cases I worked on,” he writes, naming nine such victims, including Emmett Till and the Rev. James Reeb, whose deaths remained unpunished. But Mitchell is too harsh a judge of his own record, for no other journalist has made a greater contribution to cold-case investigations than has he.

Race Against Time

A Reporter Reopens the Unsolved Murder Cases of the Civil Rights Era

By Jerry Mitchell

Simon & Schuster. 421 pp. $28