Mexican officials continue to investigate the death of an Iowa family from Creston, Iowa.

TULUM, Mexico — Propane from a faulty water heater asphyxiated an Iowa family that died during spring break, Mexican police said.

In an interview Wednesday with The Des Moines Register, Christopher Martínez, the main investigator on the case for the Fiscalia General Office in the Tulum municipality, laid out what police know of the last days of Kevin, Amy, Sterling and Adrianna Sharp of Creston, Iowa.

The family had been staying at the luxury Tao Mexico vacation community near Akumal, on the east coast of the Yucatan Peninsula, when they died.

The initial autopsies, conducted in nearby Playa del Carmen, show the four Iowans died of asphyxiation from propane inhalation, he said. The water heater in the condominium, which used liquid propane for fuel, had rusted in the humid Caribbean climate.

Exposure to very high concentrations of propane can cause death from carbon monoxide poisoning, essentially suffocation, according to National Institutes of Health.

“There was a leak, and it was coming right from the laundry room,” he said through an interpreter. “The laundry room had no ventilation whatsoever.”

Samples from the autopsy were sent to Mexico City for further analysis. Those results have not been returned to local police, Martínez said.

Police found the bodies in a top-floor condominium about 3 a.m. March 23. The next day, investigators combed through the apartment wearing full body suits and respirators.

When police took apart the water heater, they discovered rust had corrupted the device, a common problem for appliances in this part of the Caribbean, police said. They examined a similar model for comparison.

The appliance, a Delta Raptor, was purchased in 2012, and its warranty expired in 2017, Martínez said.

Jana Weland, Amy Sharp’s cousin who has served as a family spokeswoman, said Wednesday her family knew the water heater was the suspected source of the gas leak, but that American and Mexican officials had not notified them about what the four inhaled.

They have not received calls from the U.S. Consulate in the area, she said.

“No one has contacted the family and told them exactly anything yet,” said Weland, who also lives in Creston. “It is frustrating for the family because we have not gotten anything final.”

In a written statement, the State Department said that after a death abroad it assists with returning remains to the United States, provides a report based on the local death certificate and can provide other assistance to next of kin if needed.

In his plain, white-walled office surrounded by 2-foot-tall stacks of police investigative files and binders, Martínez flipped through fire department photos showing how investigators discovered the apartment.

The pictures, which he would not allow to be published, show black marks on the laundry room walls and ceiling surrounding the rectangular water heater tank. A fire never broke out, but the water heater malfunction stained the walls, Martínez said.

Investigative photos show a typical vacation scene. The unit features bright tropical artwork and a lush area rug under the dining table. The place looks lived in: Boxes of cereal line the kitchen island, clothes await washing in the laundry room, and opened Coca-Cola and water bottles sit on the counter tops.

Martínez wouldn’t say who owns the condominium. The homeowners’ association has said the current owner is responsible for all maintenance of the unit. 

Weland said her family was told the condominium was purchased in 2013 by someone living in the United States though she does not have the owner’s name.

Police believe that the Sharps had been at the beach on the day of their deaths. Their rental car was full of sand. Police believe the family returned to the condo to bathe and rest.

Each parent was found in a separate bedroom — both apparently had been sleeping — and the children, ages 12 and 7, were found in front of the television in the living room.

Martínez reiterated that police do not believe any foul play was involved. The apartment showed no signs of a break-in or struggle, and the bodies were undisturbed.

“They were totally relaxed, like if you go to sleep and stay in one position,” he said.

Police still do not know an exact time of death. The autopsy analysis in Mexico City should shed more light on that, Martínez said.

The air conditioning unit in the condominium was in use, which likely slowed decomposition of the bodies.

“This will be clear once the autopsy is finished,” he said through the interpreter.

The Sharps were supposed to check out of the condominium March 21, return their rental car at the Cancun International Airport and fly home. The rental car company had a credit card on file and was unconcerned that the Sharps had missed their return date, Martínez said.

Renters typically left their keys in their condos at the Tao complex when checking out rather than returning them to a receptionist, he said.

“The only thing with a question mark is why they did not go to the condo for cleaning,” he said.

Municipal, state and federal officials are working together on the case. No one in the Quintana Roo state has ever died in similar conditions, Martínez said.

Deaths like those of the Iowa family tend to attract heavy attention from Mexican authorities because of the importance of tourism to the area. With popular destinations like Cancun, Playa del Carmen and the Riviera Maya region, Quintana Roo state is one of the most heavily traveled parts of the country.

Martínez said he wanted Americans to know the Sharps’ deaths were a “totally isolated” accident. Tourists in the Riviera Maya are “well taken care of.”

“It is important to know this wasn’t a crime. It’s just something unfortunate that happened,” he said. “It’s something that could happen in the United States or anywhere.”

After reading last month that a water heater had been blamed in the Sharps’ deaths, a Canadian man contacted The Des Moines Register with information about a similar incident he encountered while vacationing several years ago at the exclusive Tao community.

Garnet “Todd” Johnson, 54, of Saskatoon, Saskatchewan, said he complained of problems with his gas water heater to a property manager at Tao.

A pipe fitter by trade, Johnson said he smelled gas in his luxury condominium. He grew so concerned that he shut off the propane and turned it on only when he needed to run the shower.

“As soon as you opened the door to the laundry room, you could smell it,” he said.

The woman he had rented from complained that she had been fighting the Tao property managers for months to get it repaired.

When a Register reporter contacted Tao homeowners association officials Tuesday, they declined to comment. Johnson, who stayed in a building near the Sharps’ rental, said he could not believe the news when he learned they had died from a water heater gas leak.

“I just felt sick to my stomach,” he said. “Having trouble with our water heater and then seeing that a family is dead because of a water heater, it’s like, what the hell?”

Contributing: Luke Nozicka, The Des Moines Register. Follow Kevin Hardy on Twitter: @kevinmhardy