BROOKLYN — NXIVM co-founder Keith Raniere is scheduled to stand trial alone next month after the last of his five co-defendants — Seagram's liquor fortune heiress Clare Bronfman and Kathy L. Russell, a longtime bookkeeper for NXIVM — pleaded guilty to federal criminal charges on Friday.

Their guilty pleas leave the secretive man known to his followers as "Vanguard" suddenly facing the prospect of having his staunchest confidantes testify against him in a racketeering case that dismantled his stealthy and, according to prosecutors, inherently criminal and "cult-like" organization.

Raniere, 58, has for more than a year maintained his innocence while being held without bond in a federal detention center in Brooklyn — cut off from communicating with his former followers, including his co-defendants.

The government's case has now been buttressed as Raniere's five female co-defendants all admitted to or were charged with various crimes, including coercing women to perform labor and to have sex with Raniere; holding a young Mexican woman in a room against her will for nearly two years; hacking computers to spy on their enemies or to check the loyalty of other followers; manipulating evidence in a federal court proceeding; forging identity documents; money laundering and visa fraud.

For Raniere, the potential fallout of a conviction is more consequential because the indictment includes allegations that he sexually exploited a 15-year-old girl and possessed child pornography — naked photographs of that teenage girl. Those accusations carry a potential mandatory minimum prison sentence of 15 years.

Bronfman, who was NXIVM's operations director and one of its largest financial contributors, and Russell, who oversaw their tax and business filings, both pleaded guilty Friday in back-to-back proceedings in front of a U.S. District Court Judge Nicholas G. Garaufis in Brooklyn.

Bronfman, 40, whose charged crimes included identity theft, money laundering and visa fraud, pleaded guilty to two counts, conspiracy to conceal and harbor illegal aliens for financial gain and fraudulent use of identification — acknowledging that she had given credit card number information of a dead person to Raniere in order to help him avoid taxes.

She faces between 21 and 27 months in prison at her sentencing on July 25, and agreed to forfeit $6 million.

Looking frail and speaking softly in a slight English accent, Bronfman told Garaufis she had "received a great gift from my grandfather and my father that does not come with the ability to break the law; it comes with great responsibility to uphold the law."

"I am truly remorseful," she said. "I endeavored to do good in the world and help people — however, I have made mistakes."

Russell, 61, had been accused of falsifying identity documents to help smuggle a Mexican woman across the Canadian border, and of facilitating the installation of a "key-logger" device on the computer of a NXIVM accountant to monitor his emails. On Friday, she pleaded to a single count of visa fraud related to a letter she wrote that included bogus data about a NXIVM associate, Loretta Garza.

Russell signed a plea agreement that calls for her to spend up to 12 months in prison. She began choking up after the judge asked her if she understood she was waiving her right to trial.

"I know what I did was wrong," she said. "I'm very sorry for the trouble I have caused. I have compromised my own principles, and I'm going to have to live with that for the rest of my life."

The admissions on Friday by Bronfman and Russell followed guilty pleas over the past month by former television actress Allison Mack, 36; Lauren Salzman, 42; and NXIVM president and co-founder Nancy Salzman, 64.

The federal investigation of NXIVM broke open in March 2018 when Raniere and Mack were arrested on federal criminal charges. In July, federal agents in Albany arrested the Salzmans and Russell. Bronfman was taken into custody that same day by federal agents in New York City.

The guilty pleas signaled the unraveling of Raniere's control of his close-knit and ultra-secretive organization that he and Nancy Salzman had built over the past 20 years. With the help of millions of dollars from Bronfman and her sister, Sara, who was not accused of wrongdoing, NXIVM and its associated entities lured thousands of followers into "executive success" training programs that prosecutors have cast as no more than a "cult-like" pyramid scheme, according to court filings.

The organization also immersed itself in side efforts, including allegedly unsanctioned and disturbing "brain studies" that Raniere has indicated were intended to help find a cure for Tourette syndrome and other medical conditions.

A superseding indictment unsealed in March against Raniere and four of his co-defendants — Nancy Salzman had pleaded guilty by then — had added seven charges, including some leveled at Raniere for his alleged sexual exploitation of the underage girl.

Several criminal counts against Raniere were dropped by federal prosecutors in Brooklyn, which is part of the Eastern District of New York, because the alleged crimes took place in the Capital Region, which is part of the Northern District of New York. Federal prosecutors in Albany are reviewing the charges, including a sexual exploitation allegation, and have the option to prosecute Raniere in Albany as part of a separate case.

Several of the federal criminal charges in the indictment center on a secret club within NXIVM that Raniere founded and had claimed was a private women's organization to help its members improve their lives. Instead, prosecutors said, women were lured into the club, known as "Dominus Obsequious Sororium," which means "Master Over the Slave Women." Many did not know that Raniere was the group's "grand master."

Mack had a pivotal role in that club, prosecutors said, and allegedly helped gather "collateral" from the women who joined. If they tried to leave, they were threatened that their collateral — sometimes damaging information about family members, or close-up photographs of their genitalia — would be released. Some of the women were allegedly branded with a symbol that combined the initials of Raniere and Mack, and coerced to have sex with Raniere.

Lauren Salzman also had an integral role in the DOS club, including hosting pre-branding ceremonies at her Halfmoon residence, where the women were blindfolded before being driven to an undisclosed location — a nearby townhouse — and cauterized by a physician, Dr. Danielle Roberts.

Raniere and Mack both were charged with multiple counts of sex trafficking, conspiracy to commit sex trafficking and conspiracy to commit forced labor.

Mack had allegedly made some of the women pose for nude photographs that she would forward to Raniere. She also delivered some of the women to Raniere for sexual encounters, and at least one alleged victim described the sex as unwanted.

NXIVM has been described by experts as a cult. Raniere, in statements posted on NXIVM's website two years ago, characterized the slave-master group as a consenting, private "sorority" and said that he and the corporation had no role in it.

Opening statements in Raniere's criminal trial are scheduled to take place May 7 in Brooklyn. He remains in custody at a federal detention facility in Brooklyn without bond.

After Bronfman's appearance Friday, Raniere's attorney Marc Agnifilo said outside the courtroom that the defense team was "glad the trial is finally starting."

"We feel we have something of an uphill battle, but Keith is focused on his defense," Agnifilo said, adding that Raniere has "no intention of pleading guilty."

Correction: An earlier version of this story incorrectly stated Clare Bronfman and Kathy L. Russell had pleaded guilty to racketeering charges. Also, Bronfman's sentencing date was incorrect.