Rick Alan Ross is an expert on cults who has assisted with over 500 interventions across the globe.

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The author of “Cults Inside Out: How People Get In and Can Get Out" says that the Peoples Temple at Jonestown which was founded and lead by the Reverend Jim Jones is an example of a destructive cult in the worst possible sense.

WATCH Cult Leader’s Former Body Guard Claims Jim Jones Was ‘A Prisoner Of Jonestown’

In November 1978, over 900 of Jones’s followers died at the settlement in remote Guyana. Reportedly, many of the dead voluntarily drank cyanide-laced fruit punch, while others were forced into ingesting the drink, injected with the poison, or shot.

“I think the single most salient feature of a destructive cult is that the leader becomes an object of worship,” says the author, who identifies Jones as both the “defining element” and “driving force” of the Peoples Temple.

Watch the video above as Ross explains how Jones knowingly used “identifiable methods of manipulation” in order to control his followers, and described the outside world in negative ways to create “incredible fear, which he used to leverage his own power in the group.”

Then on Wednesday’s Dr. Phil, hear from Jonestown survivors and someone who was once part of the cult leader’s inner circle. Check here to find out where you can watch.

This program contains disturbing images. Viewer discretion is advised.

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Congresswoman Jackie Speier Shares First-Hand Memories Of Events Surrounding 1978 Jonestown Massacre