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A retired security guard was behind bars Monday for allegedly killing a retiree in northern San Diego County more than three decades ago.

“A promise was made 32 years ago by the daughter of the decedent, that we would find and bring the killer to justice and that’s happened,” Escondido Police Department Chief Craig Carter said.

Nathan Eugene Mathis, 62, was arrested last week at his Ontario home in connection with the fatal stabbing of 75-year-old Richard Finney of Escondido, KTLA sister station KSWB in San Diego reported.

On the morning of Nov. 13, 1986, Finney was found stabbed to death in his living room at the apartment where he lived by himself, Lt. Ed Varso said. Money, jewelry and other miscellaneous items belonging to the victim had been stolen.

Detectives who initially investigated the homicide collected evidence at the crime scene, including two knives used in the deadly assault, fingerprints and blood. They were unable to identify a suspect, however, and the case eventually went cold, the lieutenant said.

In 2007, Escondido Police Department cold-case homicide investigators Chuck Gaylor and Norman Wight reopened the investigation.

“Technological advances not available in 1986 allowed them to have further testing completed on the previously collected blood evidence,” Varso said. “The testing revealed the DNA profile of a potential suspect.”

The newly obtained information was compared with known genetic profiles in a national database but resulted in no matches.

“It’s incredibly frustrating because having a bloody palm print with two DNA profiles, suspect and victim’s blood on this blood print it’s basically having the silver bullet for a case,” said retired Escondido police Sgt. Chuck Gaylor.

In 2016, Escondido police forensic fingerprint expert Cassaundra Barnes used new technology that allowed for a better quality photograph of a fingerprint collected from Finney’s apartment. The improved image, in combination with advances in fingerprint comparison databases and comparisons of DNA with the genetic material collected from Finney’s apartment in 1986, led to Mathis’ identification as a suspect in the case.

Mathis was booked into county jail in Vista, where he is being held on a $3 million bail.

The motive for the slaying remains unclear, the lieutenant said.

Though Mathis lived in northern San Diego County at the time, there is no evidence that he knew the victim or had met him prior to the homicide, according to Varso.