(KTLA/NEXSTAR) – Two Americans vacationing in Mexico were found dead in their hotel room on Tuesday, and autopsies now suggest the cause of death to be “intoxication by an undetermined substance,” according to prosecutors in Mexico’s Baja California Sur.

The findings align with earlier statements from local police. A friend of the couple also said she was told the couple had died of carbon monoxide poisoning, in an account she shared in an online fundraiser created earlier this week.

The bodies of John Heathco, 41, and Abby Lutz, 28, were discovered inside a room at the upscale Hotel Rancho Pescadero in the village of El Pescadero around 9 p.m. Tuesday, the Baja California Sur Attorney General’s Office previously confirmed to ABC News.

The couple had been dead for 10 or 11 hours before they were found, prosecutors said.

El Pescadero is located on the Pacific coast of the Baja Peninsula, roughly one hour north of Cabo San Lucas.

According to his LinkedIn profile, Heathco, a resident of Newport Beach, was the founder of LES Labs, a nutritional supplement company. Lutz, originally from Salt Lake City, Utah, worked as a nanny, according to her Facebook page.

In a GoFundMe post, a friend of Lutz’s claimed she was informed the couple suffered carbon monoxide poisoning.

“Abby and her boyfriend thought they had food poisoning and went to the hospital to get treatment. We were told they were feeling much better a few days later,” Gabrielle Slate, the organizer of the online fundraiser, wrote. “We received a phone call saying that they had passed away peacefully in their hotel room in their sleep. We have been told it was due to improper venting of the resort.”

A manager at the resort has since claimed there was no evidence of dangerous gas found in the couple’s room.

“We continue to cooperate with authorities as they conduct their investigation to understand the cause of this terrible tragedy,” Henar Gil, the general manager of Rancho Pescadero, said in a statement. “We understand authorities immediately tested the air quality in the room after responding to the situation, and at the time, did not report any findings of gas or carbon monoxide and advised that the hotel was cleared to continue normal operations. The hotel continues to monitor air quality.”

The hotel has currently closed off the portion of the resort where the couple had stayed, Gil said.

Former and current employees of the resort, meanwhile, told the Los Angeles Times that managers at Rancho Pescadero were aware of gas leakage problems, and had even disabled carbon monoxide detectors in January. The outlet also included an account from a guest who claimed he was overcome by the smell of gas, as well as a current employee who alleged that a housekeeper was recently sickened while working in the same room where the couple was found dead.

“Housekeepers reported gas leaks, security reported gas leaks, maintenance workers reported gas leaks,” the employee claimed.

The Associated Press contributed to this report.