The FBI’s Cold Case Initiative is investigating the 46-year-old case of a Massachusetts minister who was beaten to death in Alabama while doing civil rights work, a spokesman said Friday.

The Rev. James Reeb, a Unitarian Universalist minister from Boston, was among a group of ministers who traveled to Alabama in response to the Rev. Martin Luther King Jr.’s invitation to join the Selma-to-Montgomery march.

The FBI launched an initiative in 2007 to investigate unsolved murders from the civil rights era. A spokesman with the agency, Chris Allen, said Reeb’s case is one that is currently open.

The lead state prosecutor for Selma, District Attorney Michael Jackson, said he has met with FBI agents at least twice about the case. He said the agency is actively investigating.

Reeb and two other white ministers had just finished dinner at a historically black restaurant in downtown Selma when they were attacked by a gang of whites on March 9, 1965. The city was a center for voting rights demonstrations by blacks and white supporters at the time.

Reeb, 38, died two days later, leaving behind a wife and four children.

Three white men — Elmer Cook, William Stanley Hoggle and Namon O’Neal “Duck” Hoggle — were tried on state murder charges and acquitted by an all-white jury.

The district attorney said at least one suspect in the case is still alive and in the Selma area. Like all cold cases, it will be difficult to prosecute because some of the suspects and witnesses have died, he said.

Jackson had success in another cold case last year. He got a former state trooper, James Bonard Fowler, to plead guilty in November to second-degree manslaughter in the shooting death of Jimmie Lee Jackson at a civil rights protest in Marion in 1965. Fowler is serving a six-month sentence.

The district attorney said he couldn’t pursue the Reeb case in state court because of the acquittal of the three suspects and double-jeopardy issues.

“The feds are going to have to be the ones to pick that one up,” he said.

The renewed investigation was first reported by The Anniston Star and the The Clarion-Ledger of Jackson, Miss., which collaborated through the Civil Rights Cold Case Project, which brings together reporters and documentary filmmakers on stories about unsolved civil rights killings in the South.