Royal Bahamas Police Force confirmed on Tuesday that three American tourists found dead at a Sandals Resort in May were killed by carbon monoxide poisoning.

The three tourists — Michael Phillips, 68, and Robbie Phillips, 65, from Tennessee; and Vincent Chiarella, 64, from Florida — were found dead by employees of Sandals Emerald Bay Resort in Great Exuma on May 6. Investigators were not able to immediately determine the cause of death.

“At this juncture of the investigation, we can officially confirm that all three of the victims died as a result of asphyxiation due to carbon monoxide poisoning,” the Royal Bahamas Police Force said Tuesday in a statement.

The three Americans had been found unresponsive. Investigators collected samples to see if there were any contaminants. There was no suspicion of foul play related to the incident, police added in a statement in May.

Along with the three deaths, Chiarella’s wife, Donnis Chiarella, 65, was airlifted to HCA Florida Kendall Hospital in Miami. She was listed in serious condition, then later upgraded to fair condition, and then released on May 13, according to the hospital.

On Wednesday, a spokeswoman for Sandals Resorts said the company had “fully supported the investigation into this event to ensure we are doing everything possible to learn from it.”