Authorities in the US state of New Mexico have ruled out a gas leak in the mystery deaths of actor Gene Hackman and his pianist wife Betsy Arakawa.

The Santa Fe County Sheriff’s Office said the New Mexico Gas Company confirmed “no significant findings” in its extensive investigation for gas leaks and carbon monoxide at the couple’s home, where the couple and one of their dogs were found dead on February 26.

During the examination, a “minuscule”, non-lethal leak was found in a stove burner, and four code enforcement violations were found for installation of lighters for a water heater and fireplaces. None related to gas leaks or carbon monoxide.

“Those results are not believed to be a factor in the deaths of Gene Hackman, Betsy Arakawa or their dog though the information was relayed to the Office of the Medical Investigator for consideration,” the Santa Fe Sheriff’s Office said.

The office will give an official update into its investigation on Friday (local time).

Oscar-winning Hackman’s pacemaker last recorded nine days before the 95-year-old was found dead on February 26 in a mud room in his home. The bodies of his 65-year-old wife and one of the couple’s dogs were found in a bathroom in the house.

Both bodies were in an advanced state of decomposition.

Authorities have not yet determined the cause of the couple’s death, but last Friday (US time) they tested negative for carbon monoxide poisoning.

In another curious development, the dog found near Arakawa’s body was apparently misidentified by local sheriffs.

The owner of the Santa Fe Tails, pet accommodation that has taken in the couple’s two surviving dogs, has told Fox News the dead dog was a different breed than listed in the search warrant affidavit.

Hackman and Arakawa had three dogs – Zinna, Bear and Nikita.

“Zinna was a mutt… a mixed breed,” Santa Fe Tails owner Joey Padilla said.

“Bear is the purebred German shepherd and Nikita’s the shepherd mix.”

Padilla said Nikita was distressed by the events that had unfolded at her home.

“Nikita’s the shepherd mix, and she was the one that was really terrified of what was going on when all of this was happening. She was really difficult,” he said.

Padilla said that the dog who died was Zinna, a 12-year-old reddish Australian Kelpie mix. He said Zinna was found in her crate with the door closed.

Santa Fe County Sheriff’s Office spokesperson Denise Womack-Avila acknowledged that the dead dog had been wrongly identified.

“Our deputies, they don’t work with canines on a daily basis,” she said, according to The Associated Press.

Official results of the autopsies and toxicology reports for Hackman and Arakawa are still pending.

There were no signs of blunt force trauma.

The couple’s bodies were found by a maintenance worker, who reported the front door of their house was open when he arrived to do regular work.

He and another worker later told authorities that they rarely saw Hackman or Arakawa. Their last contact was about a fortnight earlier.

There were no signs of forced entry to the house, nor that it had been rummaged through.

-with AAP