A genealogy database used to match a family's DNA with evidence found at a 1973 crime scene has led investigators to identify the long-dead suspect in the strangulation killing of a young married couple, a Montana sheriff said Monday.

Linda and Clifford Bernhardt, both 24, were killed at their Billings-area home in a case that would stymie investigators for decades.

Investigators now believe they were killed by Cecil Stan Caldwell, a longtime city of Billings employee who was once a co-worker of Linda Bernhardt, Yellowstone County Sheriff Mike Linder said. He did not identify a motive in the killing.

Caldwell had no criminal record, and died in 2003 at the age of 59, according to his obituary in the Billings Gazette.

Relatives of the victims attended a news conference in which Linder named Caldwell as the suspect. The family issued a statement thanking the sheriff's office for its work, but made no further comment and asked for privacy.

Clifford Bernhardt was a concrete worker and Vietnam veteran and his wife worked at a grocery distribution warehouse. They had been married several years and moved into a new house just weeks before they were killed.

Linda Bernhardt had been bound and sexually assaulted before her death, and authorities used psychologists to try to build a profile of the suspect, according to reports at the time.

Hundreds of interviews were conducted, and police at one point even brought in a psychic in their desperate search for clues to a crime described in a newspaper article as "the most sensational unsolved murder case in Billings history."

They also enlisted the help of "The Amazing Kreskin," when the mentalist visited town, according to a 1980 news report.

Scott Goodwin, a volunteer with the cold case unit who helped with the investigation, said he and others involved were unwilling to let it go.

"We were obsessed with it," Goodwin said. "These are two young people who didn't deserve what happened to them. They didn't do anything. They came home on a Tuesday night and they were murdered."

All other leads had dried up by 2004, when DNA was discovered on evidence gathered at the crime scene, Linder said.

But comparing that DNA against an FBI database of known criminals yielded no results, leaving authorities frustrated yet again.

In 2015, the sheriff's cold case unit enlisted a Reston, Virginia, technology company, Parabon NanoLabs, to analyze the DNA by comparing it to genetic samples available through a public genealogy database. That process ultimately narrowed the list of suspects to Caldwell and his brother, who is still alive and living outside the area, said Vince Wallis, a former detective captain with the sheriff's office who now works for the Billings Police Department.

After DNA was obtained voluntarily from the brother, it was analyzed by the Montana State Crime Lab to eliminate him as a suspect. That left only Caldwell, Wallis said.

Wallis added other circumstantial evidence including "unspecified behavior" by Caldwell connected the suspect to the crime scene, but he declined to offer additional details.

An anonymous donor in 2013 had offered a $100,000 reward for information leading to the arrest and conviction of the couple's killer.

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