Inside a 'Bizarre' Cult That Led to 5 Murders: 'Every Day Something Worse Would Surface'

In August 2000, the discovery of two people shot to death in a secluded Marin County, California, studio apartment set police on a scramble to find who killed them.

The apartment belonged to Selina Bishop, the daughter of blues rocker Elvin Bishop. One victim was Selina’s mother, Jenny Villarin, a 45-year-old bartender, while the other was Villarin’s longtime friend, 54-year-old Jim Gamble.

“For the first few hours it was kind of a what-the-heck-possibly-happened-here,” sheriff’s detective Sgt. Fred Marziano tells PEOPLE. With the 22-year-old Selina absent from the scene, “we knew we had a least a missing person. We weren’t sure if perhaps she was involved with this murder or if she herself had been a victim of foul play.”

That same August morning, authorities also learned of a missing elderly couple. The daughter of Ivan, 85, and Annette Stineman, 88, hadn’t heard from her parents in several days and found things amiss when she arrived at her parents’ home.

Their minivan later would be reported abandoned. But a more gruesome find was yet to come.

On Aug. 7, four days after officers responding to the report of gunshots had discovered the bodies of Villarin and Gamble, a man riding a Jet Ski in the Mokelumne River in Sacramento County spotted a duffel bag in the water.

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“I got a phone call from a Sacramento County sheriff’s detective asking me about the case that we were currently working on, and I was told that the duffel bag had been found and inside the duffel bag were various body parts,” Marziano says in the latest episode of People Magazine Investigates, which examines the killings and the murderous cult that soon would be tied to them.

(The episode, titled “Children of Thunder,” airs tonight at 10 p.m. ET on Investigation Discovery. An exclusive clip is shown above.)

RELATED: Inside the Murderous Plot of a Stockbroker Turned Killer Cult Leader

“You had older male parts mixed with younger female parts, and older female,” he says.

Eventually a total of nine duffel bags with dismembered remains would be recovered.

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“It was just bizarre, and every day something worse would surface,” says Marziano.

Working through their investigation, police soon turned their attention to Glenn Taylor Helzer, a 30-year-old former stockbroker and self-proclaimed prophet, and his two housemates and followers — his younger brother, Justin, 28, and Justin’s girlfriend, Dawn Godman, 26.

The group, investigators learned, had dubbed themselves the Children of Thunder and had a plan to overtake the Mormon church.

But how was this connected to the killings — and what was the group’s connection to the victims?

People Magazine Investigates: Children of Thunder airs tonight (10 p.m. ET) on Investigation Discovery.