(CNN) -- Defense attorneys in the manslaughter trial of self-help author James Ray say the state suppressed key evidence that could have helped their client and are asking a judge to declare a mistrial.
Ray is accused of manslaughter in the deaths of three people at his October 2009 "Spiritual Warrior" retreat in the desert. At least 15 others who took part in the sweat lodge ceremony became ill. More than 40 other people were uninjured.
Defense attorneys filed a motion Monday accusing prosecutors of intentionally withholding a report from environmental expert Richard Haddow, which suggests the faulty design of the sweat lodge caused or contributed to the deaths.
A hearing on the motion is scheduled for Wednesday.
Haddow's findings were in a report that was e-mailed to lead detective Ross Diskin almost a year ago, on April 29, 2010.
Ray's attorneys first learned about Haddow when he was listed as a potential witness in late October 2010. Since November of that year, they say they asked prosecutors for Haddow's report four times. They got it last week.
Though the state decided not to call Haddow as a witness at the trial, Arizona's discovery law requires prosecutors to provide the expert's report. There is also an ongoing obligation by prosecutors to turn over all material that could exonerate a defendant.
Because they are receiving Haddow's report several weeks into the trial, and because that testimony could have had a profound impact on their strategy, defense attorneys argue the judge has no choice but to grant a mistrial.
Prosecutors argue 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.
The sweat lodge ceremony consisted of eight rounds, with each round lasting 10 to 15 minutes. While they were not prevented from leaving, participants have said they were told to wait until the breaks between rounds.
Ray's attorneys have argued the deaths were accidental and 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 fatalities.