Authorities believe Oscar-winning actor Gene Hackman may have died on February 17, when his pacemaker recorded its last reading. Hackman and his wife, Betsy Arakawa, were found dead on their property this week.The cause of death of Oscar-winner Gene Hackman and his wife, Betsy Arakawa, remained unknown on Friday, according to the sheriff leading the investigation Hackmanand Arakawa were found dead with one of their dogs on their property by contractors on Wednesday. At a news conference, Santa Fe County Sheriff Adan Mendoza said the medical examiner's initial examination showed no sign of carbon monoxide poisoning. Carbon monoxide is a colorless and odorless gas produced from kitchen appliances and other fuel-burning items; it can be fatal in poorly ventilated areas. Mendoza also said an examination of 95-year-old Hackman's pacemaker saw it last recorded activity on February 17, which means he may have died nine days before he was found. What could have caused Hackman and his wife's deaths? Hackman was found in an entryway of his home while Arakawa, 65, was found in a bathroom on her side. A space heater was near her head and pills were scattered next to an open prescription bottle on the counter. Toxicology tests will be completed in the coming weeks to determine whether the pills or other drugs attributed to the deaths. Carbon monoxide has been able to be ruled out as a cause of death. Although the gas can dissipate from the environment, it cannot do so from a body, medical examiner Dr. Michael Baden said. The initial autopsies also found no external trauma to either body. Investigators searched the home and retrieved medication to treat high blood pressure and chest pain, thyroid medication, Tylenol, and records from medical diagnostics testing, court records filed on Friday showed. A 'very private' couple Investigators are seeking to find answers to the deaths they called "suspicious enough in nature to require a thorough search and investigation." They intend to comb through the couple's phones, monthly planners and reach out to family members, neighbors and workers from the gated community. It is unknown as of yet the last time anyone saw or spoke to Hackman or Arakawa. The couple was a "very private family," Mendoza said, adding that it made creating a timeline more challenging. Authorities do not believe the home had any surveillance cameras, he added. Edited by: Sean M. Sinico