What we know so far about the investigation into deaths of Gene Hackman and Betsy Arakawa

Celebrity tributes poured in after news broke on Thursday that legendary actor Gene Hackman and his wife, pianist Betsy Arakawa, were found dead in their New Mexico home.

Police say the circumstances around the deaths of Hackman, 95, Arakawa, 65, and their German shepherd were unusual, which has fuelled plenty of speculation online. The county sheriff said Friday that the couple had tested negative for carbon monoxide, but the cause of death is still unknown.

Authorities say while they do not suspect foul play was involved, they haven't ruled out the possibility as they continue to investigate. Here's what we know so far. 

When did they die? 

Santa Fe County Sheriff Adan Mendoza told reporters that Hackman and Arakawa had been deceased "for quite a while" by the time officers found them on Wednesday — possibly several days or "even up to a couple weeks."

The worker who called 911, as well as another worker, told police that they rarely saw the couple and that their last contact with them had been about two weeks before their bodies were found.

How were they found?

According to the Santa Fe County Sheriff's Office, a maintenance worker contacted neighbourhood security to conduct a welfare check after no one answered the door when he showed up at the home, a two-storey stucco building in a gated community in Santa Fe. The home's address is 1425 Old Sunset Trail, according to the county sheriff.

A security officer saw an unresponsive woman on the ground through a window and called 911.

Two patrol deputies were dispatched to the home at about 1:45 p.m. local time on Wednesday.

According to an affidavit for the search warrant, the officers spoke with two maintenance workers who said they had found the home's front door ajar. The officers confirmed the door was open when they arrived but said they did not see any signs of forced entry and that it did not appear anything was "out of place" or had been taken from the home.

Inside, the deputies found the bodies of a man and a woman, in separate rooms, both of whom appeared to have fallen suddenly.

The woman was found in a bathroom near a space heater on the ground, with a bottle of prescription pills scattered on the countertop, while a man was in the entryway with a cane and a pair of sunglasses lying nearby, authorities said.

Officers said they also found a dead German shepherd inside a kennel in a bathroom closet, about "10-15 feet" from the woman. They also found two healthy dogs — one inside and one outside the home — and said a dog door allowed them to enter and exit.

Deputies secured the scene and notified the criminal investigations division.

Because of early suspicions that the deaths were caused by carbon monoxide poisoning, Santa Fe City fire personnel and the New Mexico Gas Company were called to the scene to test for carbon monoxide and "other foreign elements."

The home was deemed safe to enter, and a search warrant was carried out at about 9:30 p.m.  

How did the couple die? 

Authorities say there are no apparent signs of foul play at this stage of the investigation.

The fire department did not locate signs of a carbon monoxide leak or poisoning, however, and the gas company found no immediate evidence indicating any problems with the pipes.

The affidavit said the bodies showed no indications of blunt force trauma or wounds, but police still sought to seize any blunt force objects during the search warrant, saying the circumstances around the deaths are "suspicious enough in nature to require a thorough search and investigation."

The sheriff's office later said initial autopsy findings noted there was no external trauma to either individual.

The cause of death will be determined by the Office of the Medical Investigator. 

Carbon monoxide and toxicology test results are pending, but they can potentially take several months.