A former Columbia University doctor who critics charged was let off easy in a 2016 no-jail plea deal in a sexual assault case has been indicted by a federal grand jury on charges of using his position to sexually abuse female patients.

The federal indictment against Robert Hadden, a former gynecologist and obstetrician at the New York City Ivy League school and at New York-Presbyterian Hospital, was unsealed on Wednesday in the U.S. District Court for the Southern District of New York, charging him with abusing six victims, including a minor prosecutors said he delivered as a baby.

But the court document says the 62-year-old Hadden, who was stripped of his medical license in 2016, sexually abused “dozens” of patients” between 1993 and 2012, including “multiple minors.”

“Hadden acted as a predator in a white coat,” acting U.S. Attorney Audrey Strauss said at a news conference on Wednesday announcing the charges.

Hadden was arrested at his home in Englewood, New Jersey, at 6 a.m. on Wednesday.

None of the victims have been named, but the wife of former Democratic presidential candidate Andrew Yang claimed in January that she was victimized by Hadden.

According to the federal indictment, Hadden allegedly used his position at Columbia University and New York-Presbyterian Hospital “to make or to attempt to make his victims believe that the sexual abuse he inflicted on them was appropriate and medically necessary.”

“Hadden did so through a process that entailed developing a relationship with his victims and causing them to trust him, before engaging in a course of increasingly abusive conduct, which Hadden attempted to mask under the guise of legitimate medical care,” the indictment alleges.

Federal prosecutors outlined a series of breast and pelvic exams that were “excessively long and sexualized” after ensuring no one else was present in the examination room.

Hadden, according to the indictment, frequently targeted women who were young and unlikely to have much, if any experience with another OB-GYN.

“For many victims, Hadden was their first gynecologist, and for others, Hadden was their doctor during their first pregnancy. In doing so, Hadden intentionally targeted victims who would not know what to expect during their exams,” the indictment alleges.

It remained unclear Wednesday if Hadden has retained an attorney to represent him in the federal case. He is expected to be arraigned in New York federal court on Wednesday afternoon.

The new indictment comes after the Manhattan District Attorney’s office decided in February to reopen a criminal case against Hadden.

Hadden pleaded guilty in 2016 to a single felony count of criminal sexual contact and a misdemeanor count of forcible touching as part of a deal that kept him out of prison. He was forced to give up his medical license.

He had initially been charged with sexually abusing 19 women.

Following Hadden’s plea deal, dozens of women have come forward with public accusations against him, including Evelyn Yang who told CNN in January that Hadden had assaulted her in 2012, while she was pregnant with her first child.

Following Wednesday’s announcement of the indictment, Evelyn Yang released a statement thanking the U.S. Attorney’s Office of the Southern District for bringing the charges against Hadden, saying “they are long overdue.”

“This physician abused dozens of women, including minors, under the guise of practicing medicine and should not be walking free,” Evelyn Yang said in her statement. “I hope that this action leads institutions like the hospital Dr. Hadden worked at for decades to take complaints of assault and abuse seriously immediately as opposed to ignoring them or brushing them under a rug for years. Thank you to everyone who made today possible. It shows that if we come forward we can make a difference.”

The Manhattan District Attorney’s office also released a statement on Wednesday, saying, “Our office provided substantial assistance leading to today’s indictment, and our continuing investigation — which examines potential failures by Dr. Hadden’s employer and hospital to disclose additional incidents of abuse to our office and to regulators when required — is intensely active and ongoing.”

Strauss, the federal prosecutor, described a pattern of conduct that enabled Hadden to abuse “dozens” of victims over a nearly 20-year period beginning in 1993. That pattern began by arranging to be alone with victims. Hadden would send nurses and medical assistants out of the room and then gain the trust of his victims by sharing information about himself, Strauss said.

“His conduct was neither normal nor medically necessary,” Strauss said as she described how Hadden “touched, squeezed, even licked his victims” during gynecological examinations that he “used for his own sexual gratification.”

Strauss commended the victims, calling them “brave women” who courageously came forward to tell their stories.

The FBI implored additional victims to come forward, saying the investigation is ongoing.

“The charges outlined today are outrageous,” said Bill Sweeney, the agent in charge of the FBI’s New York Field Office. “If you have been victimized by Robert Hadden in any way … please call us.”

In February, a spokesman for Manhattan District Attorney Cy Vance said in a statement provided to ABC News that two senior prosecutors had been assigned to reexamine the case and were “in touch with a representative of a number of survivors.”

“We admire the courage of the survivors who have recently shared their stories,” said Vance’s spokesman, Danny Frost. “Their voices will be heard and the abuse they suffered will be thoroughly investigated.

At the time, Anthony T. DiPietro, a malpractice attorney who represents several Hadden victims, issued a statement accusing Columbia University of covering up Hadden’s sexual abuse for the past 25 years.

“In order to make sure this doesn’t happen again, I’m calling for the DA to open a criminal investigation into Columbia University for the role it played in enabling, aiding, abetting, and covering up two decades of sexual abuse,” DiPietro said.