(CNN) -- A judge denied a defense motion to acquit self-help author James Ray on three counts of manslaughter Tuesday.
Kirby Brown, James Shore and Lizbeth Marie Neuman died in 2009 after participating in a sweat lodge ceremony, organized and led by Ray.
The ruling was issued by Yavapai County, Arizona Superior Court Judge Warren Darrow around 1 p.m. (4 p.m. ET).
Prosecutors allege that Ray's recklessness in operating the sweat lodge caused the deaths of Brown, 38, of Westtown, New York; Shore, 40, of Milwaukee; and Neuman, 49, of Prior Lake, Minnesota.
At least 15 others who took part in the sweat lodge ceremony became ill. More than 40 others were uninjured.
Prosecutors have argued that the lodge -- made of willow trees and branches, and covered with tarpaulins and blankets -- was heated to a perilously high temperature, causing the participants to suffer dehydration and heatstroke.
They have also said the self-help guru didn't monitor the temperature inside the lodge or the well-being of participants and was indifferent to those clearly having trouble.
Prosecutors rested their case last week.
Ray's lawyers have countered that what happened was a tragic accident, not a crime. They asked witnesses who were in the sweat lodge whether they signed a release form warning them of the dangers. All replied that they signed, but some said they didn't read the form.
Ray's attorneys also have suggested that exposure to an unknown toxin in the lodge -- perhaps a pesticide, rat poison or something in the type of wood used to heat the rocks -- could have caused the deaths.
They were expected to begin presenting their case Tuesday afternoon.
Event participants paid up to $10,000 to seek "new areas of consciousness" at the October 2009 Spiritual Warrior retreat in the desert, according to trial testimony. Many had attended previous James Ray International seminars.
In Session's Carol Gantt contributed to this report.