Gas leak from water heater likely killed American family in Mexico, official says Mexican prosecutor blames water heater as gas leak that killed Iowa family.

A gas leak from a faulty water heater is likely to blame for the deaths of an Iowa family sleeping at a seaside Mexican condo earlier this month, according to a prosecutor.

The condo's water heater "was leaking gas, maybe from use or lack or maintenance" and likely emitted "a high level" of toxic gas, Miguel Angel Pech, lead prosecutor of the coastal state of Quintana Roo, said during an interview by a local radio program operated by Grupo Formula.

Kevin Sharp and Amy Sharp, and their children Sterling Wayne, 12, and Adrianna Marie, 7, died as a result of "asphyxiation by inhalation of toxic gases," according to autopsy results.

Amy Sharp's sister, Renee Hoyt, told ABC News soon after her sister and her family were reported missing that they had flown from St. Louis to Cancun for a seven-day spring break vacation and were staying in the coastal town of Tulum.

Hoyt said she received a text message from her sister that they'd arrived at their condo. It was the last time she heard from her sister.

The Sharps were no-shows on their return flight to St. Louis on the evening of March 21.

"When they got off the plane, their instructions were to text home and let us know that you made it back," Hoyt said.

Relatives back in Iowa were still attempting to prepare for the return of the family members' bodies by Wednesday.

A relative of the Sharps told ABC News on Monday that funeral plans were pending and that "the family knows what it wants to do" but nothing had been confirmed.

The condo rented by the Sharps was located at Residencial TAO. Its homeowners association confirmed on Sunday that Mexican authorities were let into the property and ultimately found the Sharps after relatives inquired as to their whereabouts.

The homeowners association said in a statement that the vacation property shifted ownership in November 2013 to a private owner who then became "accountable for its maintenance."

ABC News' Ben Gittleson and Bill Hutchinson contributed to this report.