In 2014, when the student was visiting Ms. Uwanawich in Florida, Ms. Uwanawich admitted that the curse was a lie, according to court documents.

Soon after the student learned the truth, she reached out to Bob Nygaard, a retired New York police officer and private investigator who specializes in psychic fraud. Mr. Nygaard, who has helped prosecute at least 40 fortunetellers across the country, compiled a case for the student and took it to the Broward County Sheriff’s Office in Florida, he said.

It sat there for years until the Federal Bureau of Investigation, which he had worked with before, contacted him for advice on a different psychic fraud case, Mr. Nygaard said. When he mentioned the medical student’s case, the F.B.I. decided to pursue it.

There is a pattern among these cases, Mr. Nygaard said.

“They isolate the victim from friends and family,” he said. “Then they exacerbate already existing fears, usually related to love, money or health. Then they say they’re the only one that can help.”

Mr. Nygaard, who doesn’t believe in psychic capabilities, said these cases were not about proving whether a person actually had supernatural abilities. He said he looked for false promises and misrepresentations that can be prosecuted.

“I give her a lot of credit because she’s very brave and strong for wanting to come forward,” Mr. Nygaard said of the student. “It’s very difficult when someone pretends to be your confidante and then they pull the emotional rug out from under you.”

Ms. Uwanawich claims she was born into “Gypsy culture” and forced by her family into being a fortuneteller who would contribute all funds to the “Gypsy family,” according to court documents. She also said that her “Gypsy husband” would physically assault her if she did not swindle money for him.