Going Clear: Scientology and the Prison of Belief opens at Sundance Film Festival with police protection

Going Clear: Scientology and the Prison of Belief has premiered at the Sundance Film Festival to a packed house - not with a star-studded red carpet, but with police protection.

A week before Sunday's premiere, the Church of Scientology took out full-page ads in The New York Times and Los Angeles Times claiming the documentary is filled with falsehoods.

Based on Lawrence Wright's 2013 book of the same name, Oscar winner Alex Gibney's film claims that the church routinely intimidates, manipulates and even tortures its members, tracing the rise of the religion and its founder, former science-fiction writer L. Ron Hubbard, and his successor as head of the church, David Miscavige. Gibney also interviewed several former Scientology believers, including past executives.

Paul Haggis, director of the Oscar-winning Crash, left the church in 2009 after decades of membership. "I was really stupid. I was part of this for 30 years before I spoke out," he says in the film. "I was deeply ashamed."

As Haggis climbed "the bridge" to the most enlightened levels of Scientology, he finally learned Hubbard's ultimate theory: That a tyrannical galactic overlord named Xenu dropped frozen bodies from millions of years ago into volcanoes, and those spirits attach themselves to modern people today. Scientology is the means of ridding the body and mind of those spirits to become "clear".

Another former member who left the church in 2013 said its approach is "like brainwashing".