Actor Gene Hackman died of heart disease a full week after his wife died from hantavirus in their New Mexico hillside home, likely unaware that she was dead because he was in the advanced stages of Alzheimer’s disease, authorities revealed Friday.

Both deaths were ruled to be from natural causes, chief medical examiner Doctor Heather Jarrell said alongside state fire and health officials at a news conference.

“Mr. Hackman showed evidence of advanced Alzheimer’s disease,” Jarrell said.

“He was in a very poor state of health. He had significant heart disease, and I think ultimately that’s what resulted in his death.”

Authorities didn’t suspect foul play after the bodies of Hackman, 95, and Betsy Arakawa, 65, were discovered on February 26.

Immediate tests for carbon monoxide poisoning were negative.

Investigators found that the last known communication and activity from Arakawa was February 11 when she visited a pharmacy, pet store and grocery before returning to their gated neighbourhood that afternoon, Santa Fe County Sheriff Adan Mendoza said on Friday.

Hackman’s pacemaker last showed signs of activity a week later and that he had an abnormal heart rhythm February 18, the day he likely died, Jarrell said.

Although there was no reliable way to determine the date and time when both died, all signs point to their deaths coming a week apart, Jarrell said.

“It’s quite possible he was not aware she was deceased,” Jarrell said.

Dr Michael Baden, a former New York City medical examiner, said he believes Hackman was severely impaired due to Alzheimer’s disease and unable to deal with his wife’s death in the last week of his life.

“You are talking about very severe Alzheimer’s disease that normal people would be in a nursing home or have a nurse, but she was taking care of him until she passed away,” Baden said.

Their bodies were found a little over a week later. Hackman was found in the home’s entryway. His death was tied to heart disease with Alzheimer’s disease contributing.

Arakawa was found in a bathroom. Authorities linked her death to hantavirus pulmonary syndrome, a rare but potentially fatal disease spread by infected rodent droppings.

Thyroid medication pills prescribed to Arakawa were found nearby and weren’t listed as contributing to her death, Jarrell said.

Hantavirus typically is reported in spring and summer, often due to exposures that occur when people are near mouse droppings in homes, sheds or poorly ventilated areas. This is the first confirmed case of hantavirus in New Mexico this year.

While hantavirus is found throughout the world, most cases in the US have been found in western states. The virus can cause a severe and sometimes deadly lung infection.

Jarrell said it was not known how quickly Arakawa died.

One of the couple’s three dogs also was found dead in a crate in a bathroom closet near Arakawa, while two other dogs survived. Authorities initially misidentified the breed.

Dogs do not get sick from hantavirus, said Erin Phipps, a veterinarian with the New Mexico Health Department. The sheriff considers this an open investigation until they receive results of the dog’s necropsy and finish checking into data from personal cellphones retrieved from the home.

When Hackman and Arakawa were found, the bodies were decomposing with some mummification, a consequence of body type and climate in Santa Fe’s especially dry air at an elevation of nearly 2,200 metres.

Doctor Victor Weedn, a forensic pathologist in Virginia, said that when two bodies are found at the same time the usual assumption would be that they died at the same time.

But Hackman’s Alzheimer’s disease added a complicating factor: He apparently was unable to seek help after his wife died.

“They died several days apart: One dying of a viral infection, the hantavirus, which can kill quite quickly. And the other death occurring from heart disease. And that too can be a relatively sudden death,” Weedn said. “Their (the authorities’) explanation, I thought, was quite clear and plausible. I believe they really discovered what truly happened in this case.”

Hackman, a Hollywood icon, won two Oscars during a storied career in films including “The French Connection,” “Hoosiers” and “Superman” from the 1960s until his retirement in the early 2000s.

Arakawa, born in Hawaii, studied as a concert pianist, attended the University of Southern California and met Hackman in the mid-1980s while working at a California gym.

Hackman dedicated much of his time in retirement to painting and writing novels far from Hollywood’s social circuit. He served for several years on the board of trustees at the Georgia O’Keeffe Museum in Santa Fe, and he and his wife were investors in local businesses.