More than five decades after a second world war veteran was killed while working as a milkman in Florida, investigators say they have solved the case thanks to two people who came forward after the killer died.

Hiram “Ross” Grayam was delivering milk in April 1968 and failed to return home after work. Deputies later found his body and his milk truck deep in the woods in the Vero Beach area, the Indian River county sheriff’s office said in a news release. He had been shot several times.

The case went cold, and no arrests were made during the next 56 years.

“Through determination and the cooperation of witnesses, new leads emerged: Thomas J Williams, now deceased, had confessed to Grayam’s murder, his guilt echoing from beyond the grave,” the sheriff’s office said in a statement.

Grayam, a decorated second world war veteran who received a Purple Heart, had become “a beloved milkman” after settling in Indian River county after the war, authorities said.

A witness told deputies she saw Grayam talking to two men who were walking on the side of the road, WPEC-TV reported.

“She said that Mr Grayam engaged them in conversation, and announced that he would be back shortly,” the Indian River county sheriff, Eric Flowers, said. The two unidentified men and Grayam all left in the milk truck, he said.

Grayam’s family didn’t realize anything had happened, “except my father was a little late in coming home, and then a sheriff’s deputy, an investigator showed up”, Grayam’s son Larry, who was 16 at the time, told the TV station.

During a search of the area by ground and by air, the milk truck and Graham’s body were spotted by an airplane.

“When they arrived at the initial scene, Mr. Grayam was laying next to the milk truck with bullet wounds, killed execution style,” Flowers said.

In 2006, there were rumors that Williams might have been involved. He wrote a letter to the editor of the local newspaper “saying that he had been accused of the murder, but he denied having knowledge of it, that he wasn’t involved in it”, the sheriff said.

The case went cold again, and Williams died in 2016.

With Williams now dead, detectives got huge breaks in the case in the past two years: Williams’s ex-wife and a friend of his sister came forward, telling investigators what they knew, the Florida TV station reported.

Flowers said that the witnesses – neither of whom know each other – told investigators that Williams had previously confessed to them that he had killed Grayam.

“These folks said, ‘I would have never said anything to you before, as long as he was alive, he was a threat to me and my family, we would have never told you,’ but the fact that he is now dead gave them the courage to come forward,” Flowers said.

Detectives hope that anyone who knows about the second man seen with Grayam before he was killed will contact them.