Actor Gene Hackman was alone.

The two-time Academy Award winner didn’t make any calls and missed meals.

Medical experts say it’s possible the 95-year-old, who was in declining health and suffering from advanced stages of Alzheimer’s disease, did not even realise his wife of more than 30 years was dead in the home where he was living.

If he did, experts told the BBC, he likely went through various stages of confusion and grief, trying to wake her up before the disease caused him to become distracted or too overwhelmed to act – a process that likely repeated for days before he, too, died.

Officials in New Mexico say Betsy Arakawa, 65,died of a rare virus about seven days before Hackman perished on 18 February of natural causes.

The pair – and one of their dogs – were found dead in their Santa Fe home after neighbourhood security conducted a welfare check and saw their bodies on the ground through a window.

Authorities, at first, said the grim discovery was “suspicious enough” to launch an investigation.

Their remains were discovered in advanced stages of decomposition. Arakawa was found in a bathroom with scattered pills nearby. Hackman was found near the kitchen with a cane and sunglasses. One of their three dogs was found dead in a crate.

But a police investigation found no foul play.

Instead, the case has shed light on the grim realities of Alzheimer’s disease, which damages and destroys cells in one’s brain over time – taking away memory and other important mental functions.

Catherine V Piersol, an occupational therapist with decades of experience in dementia care, told the BBC of how Hackman may have experienced repeated periods of grief from not knowing his wife was deceased.

Piersol noted that patients with advanced Alzheimer’s disease live in the present and are unable to recall moments from the past or think forward and act.

“I imagine Gene would be trying to wake his wife up and not being successful during a period of time, then extra stimuli from the surroundings would shift his attention, like one of the dogs or something,” Piersol explained.

Later, he’d become aware of his wife’s body again and “live through it again, just as any of us would,” she said.

Although nobody will know how Hackman spent his last days, the authorities and the area’s medical examiner discussed the grim possibilities.

At a press conference last week, Dr Heather Jarrell, New Mexico’s chief medical examiner, said Arakawa died of hantavirus pulmonary syndrome (HPS), a respiratory illness caused by exposure to infected rodents. Hackman’s death was the result of significant heart disease, with Alzheimer’s disease as a contributing factor.

With the advanced stages of Hackman’s Alzheimer’s disease, Jarrell believes that it is “quite possible that he was not aware that his wife was deceased.”

His autopsy indicated that he had not eaten recently, though he showed no signs of dehydration. Officials found no evidence that he had communicated with anyone after his wife’s death and could not determine whether he was able to care for himself.

Piersol said patients with advanced Alzheimer’s are not able to pick up environmental cues like light or darkness, making it harder to determine their own schedule for eating, sleeping, or bathing themselves.

“Those cues are often no longer available to people at this stage of dementia,” she said.

Dr Brendan Kelley, a neurologist specializing in memory and cognition at UT Southwestern Medical Center, explained why Hackman might have been unable to call authorities for help. He said Alzheimer’s disease can leave patients feeling emotional discomfort without being able to act on it.

“A person might feel worried or frightened, but at the same time, they might not be mentally capable to take the actions we might normally think to do in order to alleviate that worry or concern, such as calling someone else or speaking to a neighbor,” Kelley said.

Kelley said Alzheimer’s patients experience emotions such as pain and sadness and physical needs like hunger or thirst, but struggle to identify them.

Missing meals could also increase levels of confusion and agitation.

The couple’s deaths and the shocking details about Hackman living in the home for a week after his wife’s passing have devastated the Santa Fe area, where they had lived for more than 20 years.

Jeffery Gomez, a long-time Santa Fe resident, remembered seeing Hackman around town in his different cars, always with a smile. But, hearing about his final days, Gomez says he cannot understand how no one checked on the couple for such a long time. “It breaks my heart to know he was alone so long,” he added.

A list of UK-based organizations offering support and information on some topics covered in this story can be found at BBC Action Line.