The sweat lodge at Angel Valley seemed to be covered in tarpaulins
Police are continuing to investigate the deaths of two people who collapsed during a sauna-like experience at a spiritual retreat in Arizona.
Yavapai County Sheriff Steve Waugh said that inquiries were centred on self-help expert James Ray, as police looked at possible criminal negligence.
Those who died have been named as James Shore, 40, from Milwaukee, and Kirby Brown, 38, from New York state.
Mr Ray was running the "sweat lodge" where they died and 19 more fell ill.
Mr Waugh told reporters on Saturday: "We will continue this investigation down every road that is possible to find out if there is culpability on anybody relative to the deaths of these individuals."
No-one has been charged in connection with the case.
Yavapai County sheriff's spokesman Dwight D'Evelyn told the BBC on Monday that police expected to talk over the next few days to Mr Ray, who has previously appeared on the TV shows of Oprah Winfrey and Larry King.
Mr D'Evelyn said it was likely to be at least 10 days before the authorities had anything conclusive to report because it was a complex case.
Interviews are continuing with staff and guests who were at the Angel Valley resort, near Sedona, at the time of the incident.
Reports said some of the participants had paid up to $9,000 (£5,700) for their week-long stay at the retreat, which also reportedly included a 36-hour fast.
Police said between 55 and 65 people were inside the so-called sweat lodge at the Angel Valley resort for up to two hours before many of them became ill on Thursday night.
Local TV images showed the structure to be a dome-shaped frame covered by tarpaulins and blankets.
It was gradually filled with steam generated by pouring water on to fire-heated rocks brought inside, to create a kind of ceremonial sauna used by Native American and other cultures.
Jonathan Ellerby, author of the book Return to the Sacred, has participated in sweat lodges for the past 20 years and has run his own for several years, having been mentored by a Native American healer.
He told the BBC that sweat lodges or similar practices had been used as a healing tradition in cultures across North America, Africa, Europe and Asia for millennia.
"This has been going on for thousands of years because it works and because it's safe," he said.
But, he cautioned, those running sweat lodges need to have years of training and experience both to make the structures properly and to ensure participants' well-being.
"One of the mistakes that you very often hear from people who try to create home-made 'sweats' is that they will use materials that are inappropriate and not understand the consequences," he said.
Sweat lodges are usually made from all-natural materials, he said, such as a wooden frame covered with woollen blankets and cotton tarpaulins, and plastics are always avoided.
The choice of materials is important because of potential complications involving fumes and ventilation, he added.
There will typically be eight to 12 participants in each sweat lodge, sitting cross-legged in a space that measures 10-12ft in diameter, he said.
"A ceremonial steam bath is generally a process of physical detoxification, and emotional and spiritual cleansing and purification. It's a time for prayer and intention-setting, there are usually songs and stories," he said.
"It's not, at least in my training and experience, meant to be an exercise of endurance and it's certainly not meant to be oppressive."
Mr Ellerby, who is the spiritual programme director for the Canyon Ranch Institute health resort in Arizona, said fasting was only sometimes a part of the sweat ledge experience.
The heat is typically that of a steam room at a resort, although temperatures can go higher for short periods, he said.
People with blood pressure and heart-related conditions should be careful, he added, as well as those who have certain lung conditions or suffer claustrophobia.
Police have said it may be weeks before the cause of death at the Angel Valley sweat lodge is known.