MIMS, Florida (AP) – Four Ku Klux Klan members are almost certainly to blame for the unsolved 1951 bombing murders of two civil rights activists, investigators said yesterday.

Florida Attorney-General’s Office investigator Frank Beisler would not name the suspects or confirm whether most are still alive. At least one is dead, Beisler said.

Beisler and Attorney-General Charlie Crist announced yesterday that investigators were excavating the site where Harry and Harriette Moore’s home was blown up on Christmas night in 1951 – the final phase of an investigation relaunched a year ago. They were searching for detonators and other evidence that could prove what type of explosive was used.

All the physical evidence from the FBI investigation was destroyed, leaving investigators to recreate a crime scene more than 50 years old.

Even the new investigation had grown cold until a month ago, when Beisler interviewed a man to whom one of the bombers had confessed. That interview “shook everything we’d been doing up to this point”, Beisler said. He declined to be more specific.

“We had a lot of extraneous individual leads that didn’t fit anything until that day,” he said. “We’re going to solve this case. I’m positive now.”

Moore, who organised the Brevard County branch of the NAACP in the 1930s and worked to register black voters in an area of the state then ruled by Jim Crow laws, died when his house exploded in Mims. He became the first official of the National Association for the Advancement of Colored People killed during the modern civil rights struggle. His wife died nine days later from her injuries.

The FBI and federal prosecutors closed a several-year investigation into the Moore murders in 1955, and then reopened the case briefly in 1978, without bringing any charges. In 1991, the Florida Department of Law Enforcement conducted an investigation and a subsequent review in 2003, but evidence was ruled insufficient to pursue any suspect.

Crist reopened the case late last year.

“New evidence continues to mount every day, including today,” Crist said.

Three of the suspects had previously been fingered by the FBI, but were never charged. The fourth was interviewed but never considered a suspect by any agency, Beisler said.

Beisler said the men planned the murder up to a year in advance, and waited until Harry Moore returned from a visit to his mother-in-law’s house nearby to set off the explosion. He said one was on lookout, two were in getaway vehicles and the fourth was by the house setting off the blast.

The men were members of the Florida Klan, and had previously belonged to the white supremacist group in Georgia, Beisler said.

The excavation could take from two weeks to four months, depending on how much evidence is recovered. The debris will be examined by the FBI lab in Quantico, Virginia, Beisler said.

Authorities know the suspects had experience with dynamite, and expect lab tests to show it ignited the explosion, Beisler said.

Even without further evidence from the house, investigators would have enough evidence for an indictment, he said.

The couple’s daughter, Evangeline Moore, said she hoped to finally close this painful chapter in her life.

“I was coming home the two days after Christmas. When I got off the train, this is what hit me in the face: Your father’s dead, your mother’s in the hospital,” she said. “What kind of Christmases do you think I had? What kind of Christmas do you think I still have?”