Quintana Roo State Prosecutor Miguel Angel Pech told a local radio station that investigators discovered that "gas was escaping" from the apartment's hot water boiler, which he said could have been due to poor maintenance.
Amy Marie Sharp, 38; and their children, Sterling Wayne Sharp, 12; and Adrianna Marie Sharp, 7; were found dead by authorities after conducting a welfare check Friday at in Tulum, Mexico, condominium where they were vacationing.
The prosecutor also told reporters that "a high level" of gas was found inside the rented condo.
Over the weekend, Mexican authorities said the family was killed by "asphyxia by inhalation of toxic gases", although they didn't say what type of gas had killed them and had not identified the source. Creston Police Chief Paul Ver Meer said the investigation determined that the family had not boarded the flight from Cancun, Mexico to the United States. At the time, they did not release the source of the gas. Photos published by the prosecutor's office show firemen in respirators and other workers in anti-contamination suits examining gas connections and the unit's oven. They were from Creston.
The Sharp family was found dead in Tulum on Mexico's Yucatan Peninsula, officials said.
The family had planned to meet up with some friends at a water park, Amy Sharp's cousin, Jana Weland, told ABC News.
The Quintana Roo Attorney General's Office has ruled out violence and said the family died by "asphyxiation from inhaling toxic gases". The Sharps were supposed to return Wednesday, family members said. "Even the funeral home in Mexico has been good at helping". One family member said she felt like "she lost half her family".
Besides working in beer distribution, Kevin Sharp was a race auto driver at southwestern Iowa's Adams County Speedway, where he finished fourth in last year's stock vehicle series standings.
Then the family failed to attend a basketball game Wednesday night in Danville, Illinois - a game Weland said the family was looking forward to. "All we know is that God is with us and will help us get through this".
"Creston is close-knit like all small towns in Iowa", Baldwin added.