A third person has died after falling ill in a sauna-like “sweat dome” at a retreat in northern Arizona, authorities said on Sunday.

Yavapai County Sheriff’s office said Lizbeth Neuman, 49, died on Saturday in a Flagstaff hospital after falling ill in a ceremony on October 8 at the retreat near Sedona.

More than 60 people were packed into the sweat dome at the Angel Valley Retreat Center near Sedona for more than two hours when a number of them fell ill.

Twenty-one people were taken for treatment to nearby hospitals, where two of them - James Shore, 40, and Kirby Brown, 38 - were pronounced dead.

Sheriff Steve Waugh said last week he had opened a full criminal investigation after determining that the deaths were not accidental.

The group was taking part in a five-day “Spiritual Warrior” program hosted by James Arthur Ray, a self-help guru and inspirational speaker based in California.

Sedona, 117 miles north of Phoenix, is renowned for its red rocks, which some people believe have spiritual and restorative powers. The area is a popular destination for New Age retreats.

Sweat or medicine lodges, domed or oblong structures warmed with heated stones, have traditionally been used in ceremonies by some Native American cultures.

TUCSON, Arizona (Reuters)