There are still "loopholes" to close in the investigation into Gene Hackman and Betsy Arakawa's deaths.

Although Dr. Heather Jarrell, New Mexico's chief medical examiner, revealed the 95-year-old actor died from "significant heart disease" one week after his wife Betsy, 65, passed away as a result of hantavirus - which is a rare flu-like illness carried by infected rodents - on February 11, the case is not yet closed.

Santa Fe County Sheriff Adan Mendoza said in a press conference that authorities are still continuing their investigation to close a few more "loopholes," and they will take a closer look at Gene and Betsy's cellphones in order to do so.

They are also awaiting necropsy results to help determine how their dog Zinna died.

He added: "But you know, I think it's … I think we're pretty close to the timeline, and with the information that Dr. Jarrell provided."

Dr Erin Phipps from the New Mexico Department of Health noted that canines do not get ill from hantavirus.

Dr Jarrell told reporters that because Hackman was in the advanced stages of Alzheimer's disease and "was not aware of his normal daily functioning capability" it is "quite possible" that he was oblivious to his wife's death.

It is almost impossible to know exactly when Arakawa fell ill, but it was noted that once hantavirus manifests itself, death can occur "pretty quickly" afterward.

Just two days before Arakawa's presumed date of passing, she had collected Zinna from the vets after a medical procedure had been carried out, and emailed her massage therapist before heading out to go shopping around midday.

At around 16.15 that same day, she was spotted on CCTV at a local pharmacy but that was her last known sighting.

The couple also had two other dogs, which are now staying at the pet daycare facility in New Mexico but cannot be officially rehomed until wills are read out.