(CNN) He was a WWII veteran with a Purple Heart, a wife and three children. But in 1964, he vanished, moved across the country and later took the identity of an 8-year-old boy who had died years before.

His case had confounded investigators for more than a decade. US Marshal Pete Elliott called it "one of northeast Ohio's biggest mysteries."

Now, with the help of DNA testing, some of the pieces have come together.

It's a complicated story, so let's start from the beginning.

A stolen identity

In 2002, a 76-year-old man named Joseph Newton Chandler III locked the doors and windows in his apartment outside Cleveland. He turned off the air conditioning and marked the date on his calendar. Then he went into his bathroom and took his own life.

Police discovered his body about one week later, but it had decomposed in the summer heat. No fingerprints could be lifted from the man's remains and his body was cremated.

When the name "Joseph Newton Chandler III" was run through a database, police saw the man had stolen the identity of an 8-year-old boy who died in a car accident with his parents in 1945. That's when things got interesting.

A newspaper article from December, 1945 about Joseph Chandler's death.

"Joseph Chandler never got a chance to live his life, but someone else would get to live it for him," Elliott said at a news conference Thursday.

The man who went by Chandler was an electrician and a draftsman who co-workers described as being an odd, eccentric and highly intelligent man, but a loner with no family or friends, Elliott said.

Friends said he would tell them, "they are getting close," and then he would disappear from the area, returning home days or sometimes weeks later.

Chandler also kept a packed suitcase in his apartment so he was ready to go at any moment and he died with $82,000 in his bank account.

"What he was running from, I just don't know," Elliott said.

Theorists suggested Chandler could be the Zodiac Killer, or a mysterious plane hijacker named D.B. Cooper, but the truth was that no one knew who the man had been before he took Chandler's name and identity.

Eventually, the case went cold.

A breakthrough

A young photo of the man who later stole the identity of Joseph Chandler III.

A new lead emerged in 2014, when US Marshals took over the case. They discovered that Chandler had visited a hospital two years prior to his death where a tissue sample was taken from him.

With the assistance of groundbreaking genealogical research and DNA testing, doctors discovered the man who lived for decades as Chandler likely had the last name Nicholas, or something close to that.

The trail eventually led officials to the mystery man's son in March 2018. Their DNA was a positive match. From there, it all came together.

The man who went by Joseph Chandler was really Robert Ivan Nichols. He was a WWII Navy veteran who was born in Indiana and who left behind a wife and three kids.

"Once I saw the photos I knew it was him," his son, Phil Nichols, said at the news conference Thursday.

After his ship was bombed during the war in 1945, he received a Purple Heart. Nichols' family said he burned his military uniform sometime after that. In 1964, he told his wife he was leaving the family and that they would know why "in due time."

A postcard from Robert Nichols to his parents in 1965 from Stroud, Oklahoma.

From there, a trail of postcards and letters suggests he traveled around the country, spending time in Michigan, Oklahoma and in California, where he sent his son a letter with a single penny inside in 1965. It was the last time his family would hear from him.

"I hold no animosity whatsoever," his son said. "I had always hoped that he'd found a happy life somewhere."

Nichols' parents reported him missing after he left, but attempts to locate him by authorities in California and Indiana were unsuccessful.

Recent advances in genealogical technology helped crack the case. According to Elliott, this was the first investigation in US Marshal service history that used forensic genealogy.

Questions remain

In 1978, Nichols acquired the birth certificate of Joseph Chandler. Next he got a social security card in South Dakota using the real child's birthday and both parents' names. Later that year, records show that Nichols began working as an electrician in Ohio using Chandler's identity.

A photo ID for Joseph Chandler, later found to be Robert Nichols.

What Nichols did and where he lived between California and Ohio remains a mystery, and Elliott implied Nichols may have had a sinister reason to leave his family and adopt a new identity.

"There is a reason he went missing in 1965, and assumed the identity of a deceased 8-year-old in 1978 and went hiding for so, so many years," Elliott said. "There is a reason he never contacted his family again."

Yet Robert Nichols and Joseph Chandler both have no criminal history, according to Elliott.

The man known to some as Joseph Chandler and to others as Robert Nichols didn't want to be found in his lifetime or after his death. Elliott believes that someone who knew him before he disappeared might hold the key to Nichols' mysterious disappearance.

Investigators have asked for the public's help to determine where Nichols was between 1965 and 1978 and why he left his family.

"The first part of this mystery is solved," Elliott said. "But the second part we put out to you guys."