Several female members of an alleged New York-based sex cult, including Smallville actress Allison Mack, became dangerously thin after following near-starvation diets at the direction of the group’s leader, a 12-year veteran of the group testified on Monday.

The longtime member, filmmaker Mark Vicente, is a key prosecution witness at the criminal trial of Keith Raniere, whom authorities have accused of forcing female “slaves” within his NXIVM (NEX’-ee-um) organization to have sex with him, lose weight and get branded with his initials.

Vicente, who left NXIVM in 2017, said he told Raniere that Mack seemed “broken,” and that Raniere responded, “I’m trying to break her.”

Mack, who starred in the television series Smallville for a decade, was one of five co-defendants, including Seagram liquor heiress Clare Bronfman, who previously pleaded guilty to NXIVM-related crimes.

Actress Allison Mack departs court after facing charges related to the NXIVM case in New York in April. A former member testified today that NXIVM leader Keith Raniere told him he was ‘trying to break’ Mack. (Shannon Stapleton/Reuters)

Vicente told jurors in U.S. District Court in Brooklyn that the women would push their diets even further, limiting themselves to a few hundred calories a day, as penance if they slipped up.

“There seemed to be kind of a club of young women gathering around Allison Mack, and they just didn’t look healthy,” he said.

Vicente previously told jurors that Raniere’s recruits came to view him as “some kind of god,” thanks to a sales pitch that portrayed him as a genius of unparalleled insight.

Prosecutors say Raniere traded on that status to force female “slaves” who had joined a secretive sorority within NXIVM to follow his every command. The slaves were required to submit “collateral,” such as nude photos, that Raniere then used as blackmail to coerce their compliance, according to authorities.

Seagrams heiress Clare Bronfman has pleaded guilty to NXIVM-related crimes. (Mark Lennihan/Associated Press)

Raniere’s lawyer has argued at trial that the women joined voluntarily and were never forced to do anything against their will. Raniere faces life in prison if convicted.

Raniere and his closest acolytes exercised strict discipline and control over his followers, Vicente said, forcing those who questioned his leadership to undergo training and excommunicating those who went against the group.

“Many of us became very, very careful of the words we used,” he said.

Vicente, who became the group’s unofficial videographer, told jurors last week he was asked by the group’s president, Nancy Salzman, to make videos showing Raniere in a positive light.

“I really would love it if Keith Raniere does not die a criminal in the eyes of the world,” Salzman told Vicente, according to his testimony. Salzman has pleaded not guilty.

NXIVM, which started under another name in 1998, was based in Albany, New York, and operated self-improvement centres across North and Central America.