A decorated WWII veteran was "killed execution style" while delivering milk in 1968. His murder has finally been solved.

Hiram "Ross" Grayam was a decorated World War II veteran who survived the Battle of the Bulge and witnessed the liberation of two concentration camps. After the war, he returned to Indian River County, Florida, and became a beloved milkman — only to be shot dead while on his delivery route in 1968.

Now, 56 years later, the so-called "Milkman Homicide" has finally been solved.

Thomas J. Williams, who died in 2016, has been identified as Grayam's killer, the Indian River Sheriff's Office said in a statement on Thursday. Williams "had confessed to Grayam's murder, his guilt echoing from beyond the grave," officials said while announcing that the cold case had been cracked.

Grayam, a Purple Heart recipient, had relocated to Vero Beach with his family in the 1960's and became a salesman for Borden Milk Company, CBS affiliate WPEC-TV reported. He went out to do his routes on April 11, 1968, but did not return home as expected.

A witness told deputies she saw Grayam talking to two men who were walking on the side of the road, Indian River County Sheriff Eric Flowers said at a Thursday news conference. The witness said those men eventually got into Grayam's truck and the three drove away. The milkman was never seen again.

The sheriff's office later dispatched a Piper airplane, which eventually spotted Hiram's body.

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

The victim's son, Larry Grayam, was 16 at the time.

"If you were 16 years old, they told you they found your dad's body in the woods, shot to death, how would anybody feel like that? Completely devastated," Larry Grayam told WPEC-TV on Thursday.

The station reported the case went cold for decades, until 2006 when Larry Grayam was interviewed by a local media outlet about the case — an interview that the alleged killer saw.

"2006, that was the first time we really got the information about Thomas Williams being potentially involved in this," Flowers said. "Thomas Williams wrote a letter to the editor of the newspaper after he saw the coverage that was happening, saying that he had been accused of the murder, but he denied having knowledge of it, that he wasn't involved in it."

Still, authorities did not have enough evidence to arrest Williams and the case went cold for another decade — until Williams died in 2016.

Flowers said that eventually Williams' ex-wife and a friend of his sister — who did not know each other — each came forward to say that Williams had confessed to the crime.

"These folks said I would have never said anything to you before, as long has 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. "Two independent witnesses, who both say this guy confessed to killing the milkman to them."

The sheriff's office said it has leads on who may be the second man who participated in the killing, WPEC-TV reported, and they are asking residents who may know something to call them or Crime Stoppers.

"The Cold Case Unit continues the pursue every new lead," the sheriff's office said in a statement. "Armed with the latest technology and new partnerships, they stand as beacons of hope for families like the Grayams, ensuring that no victim is forgotten, and no crime is unpunished."

In:
• Cold Case
• Florida

Stephen Smith

Stephen Smith is a senior editor for CBSNews.com.