Phoenix ? A sauna-like sweat lodge at an Arizona resort meant to provide spiritual cleansing became the scene of a police investigation Friday when more than a dozen people became ill during a two-hour session and two later died.

In all, 21 of the 64 people crowded inside the sweat lodge Thursday evening received medical care at hospitals and a fire station. Four remained hospitalized Friday evening — one in critical condition and the others in fair condition.

Authorities haven’t determined the cause of the deaths and illnesses; tests for carbon monoxide and other contaminants were negative. Yavapai County sheriff’s spokesman Dwight D’Evelyn said authorities were checking into whether any of the attendees had medical conditions or were fasting.

Among those sickened were a middle-aged man and a woman who were unconscious, according to a 911 call, and a third person who was found not breathing.

Investigators were working to determine whether criminal actions might have been a factor in the incident, D’Evelyn said.