New information points to four Ku Klux Klan members as almost certainly responsible for the unsolved homicides of two civil rights activists who died when their home exploded in 1951, Florida officials say.

Attorney General Charlie Crist (R) announced Friday that investigators had begun excavating the site of Harry and Harriette Moore's home, which was blown up on Christmas night in 1951. Detectives are searching for detonators and other evidence that could prove what type of explosive was used.

The four suspects, all members of the Florida Klan at one time, had experience with dynamite, said Frank Beisler, an investigator with Crist's office. Beisler said the major break in the recently reopened investigation came about a month ago when he 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.

"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."

Beisler would not elaborate on the interview or name the suspects, but he said three of the men had previously been suspected by the FBI but never charged, while the fourth was interviewed but never considered a suspect. At least one of the four is now dead, he said.

Moore organized 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. He died when his house exploded in Mims, about 35 miles northeast of Orlando. His wife died nine days later.

The excavation could take from two weeks to four months, depending on how much evidence is recovered. But even without further evidence from the house, investigators now have enough for an indictment, Beisler said.