NEW YORK — The plainclothes detectives had arrested the 18-year-old woman for a small amount of pot, handcuffed her and placed her in a police van. For the next 20 minutes, she told prosecutors, the detectives took turns sexually assaulting her on a hellish drive through the streets of southern Brooklyn.

A month later, the Brooklyn district attorney brought an indictment against the detectives, Richard Hall and Edward Martins, detailing a graphic sexual attack against a woman in their custody. “It is incomprehensible that two veteran NYPD detectives would commit such an outrageous act,” the district attorney, Eric Gonzalez, said.

Now, a year and a half later, the case against the two former detectives has unraveled, as video and cellphone evidence has been uncovered showing that the victim was not entirely truthful in her testimony to the grand jury.

On Wednesday, Gonzalez’s office dropped more than 40 charges against the officers that included rape, sexual assault and kidnapping. They have been newly charged with accepting sexual favors as a bribe.

The lead prosecutor, Frank DeGaetano, announced in state Supreme Court in Brooklyn that the officers had been indicted on charges of official misconduct and bribery of services, punishable by up to seven years in prison if convicted. The charges in the original indictment carried a maximum penalty of 25 years in prison.

“We are fully committed to holding these defendants accountable by vigorously pursuing the charges in this case that can be proven with independent and reliable evidence,” Oren Yaniv, a spokesman for the Brooklyn district attorney’s office, said in a statement. He added that “unforeseen and serious credibility issues that arose over the past year” made it impossible to proceed with the charges.

The woman, whom The New York Times has not identified because of the nature of the alleged crime, used profane language to express her criticism of “the system” on Twitter. “Of course crooked cops get away with RAPE charges,” she wrote this week. The woman did not attend the hearing Wednesday.

“This is a sad day for victims of sexual violence in the United States, that something like this could happen,” said the woman’s lawyer, Michael David. “She needs to get justice.”

Mark A. Bederow, a lawyer for Martins, said the sex-crimes charges “should never have been brought” in the first place. “Now we can try the case,” he said. “What’s left of it.”

Hall’s lawyer, Peter Guadagnino, said the detectives were dedicated to being police officers, even though they quit in the uproar that followed the September 2017 allegations. “They still feel hurt,” he said.

The case against the detectives began to fall apart in recent months after defense lawyers highlighted evidence from security cameras and cellphones that contradicted the woman’s statements about what she wore that night, what the inside of the van looked like and where the men drove her.

In January, prosecutors acknowledged in a letter to the court that the woman made “a series of false, misleading and inconsistent statements about the facts of this case and about collateral or unrelated matters,” and that most troubling, “she made some false statements under oath.” The letter asked the court to allow a special prosecutor to be assigned to the case.

When the judge denied the request, Gonzalez’s office shifted gears and prepared a new case for a grand jury to review, this time without the woman’s testimony, officials said. The grand jury returned an indictment on the lesser charges.

From the start, the case had presented an unusual legal challenge for prosecutors: Under a loophole in state law — one that has since been closed — it was not illegal at the time of the reported attack for the police to have consensual sex with someone in their custody. To prove rape, the prosecutors would have had to show the men used physical force or threats to compel the woman to have sex.

Up until December, the prosecutors maintained there was strong evidence the woman had been sexually assaulted. They pointed to semen found on the woman’s body that proved a sexual encounter had taken place with both men, and to evidence the woman was in handcuffs during the alleged assault. In addition, the woman had never wavered in her assertion that she had been forcibly raped.

Yet the mounting evidence that the account the woman had given to the grand jury was not accurate put the district attorney’s office in a bind. Under their own rules of ethics, prosecutors could not permit the woman to testify at trial about parts of her story they knew were false; but if she changed her account, the defense would point it out on cross-examination, painting her as a liar.

The woman has also pursued a lawsuit and while testifying in those proceedings, she has contradicted several elements of her earlier account, court documents show.

It is not uncommon for rape victims, because of shame or trauma, to make incomplete or inconsistent statements after their attacks. Prosecutors generally work hard to thoroughly vet and corroborate a victim’s story before letting her testify to a grand jury, even when they are sure a crime has been committed.

Police reports made public in court filings show prosecutors knew about some evidence that undermined the woman’s account before they sought an indictment, defense lawyers said.

Bederow — Martins’ lawyer — said the district attorney’s office had rushed the case, allowing the woman to testify to a grand jury before they had corroborated her account with location data from the officer’s cellphones, among other things.

According to court records, shortly after 1 a.m. on Sept. 16, 2017, the woman walked into Maimonides Medical Center in Brooklyn and said that two undercover detectives had brutally attacked her. Court papers show that a triage nurse immediately called 911. Within a few hours, two officers from a local precinct and a team of detectives from the Internal Affairs Bureau showed up to interview the woman.

Over the next three days, she spoke to the authorities at least six times. Although her story sometimes shifted, with different details about what her alleged assailants did to her and who had done it first, her basic account remained unchanged.

The woman said that the former detectives pulled her over at about 8 p.m. the night before, while she was driving with two male friends in Calvert Vaux Park, near Coney Island. After they found drugs in the car, she said, they handcuffed her, placed her in an unmarked van and drove away.

She told the police several times that she was wearing a miniskirt that night, which made it easy, she explained, for the men to sexually assault her as they left Coney Island and drove up the Belt Parkway as far north as Bay Ridge. She also said she remembered the specific route because she recognized some landmarks: the Verrazzano-Narrows Bridge and her grandmother’s apartment on Shore Road.

But by 2 p.m. on the first day of their inquiry, investigators found security camera footage showing the woman leaving the police van in sweatpants, not a miniskirt, according to a detective’s report in the court record.

Hours later, court papers said, investigators also found the van, which did not quite match the description she had given. The van had bucket seats, not bench seats, as the woman had repeatedly recounted. She had also recalled seeing a laptop on the dashboard of the van, but there was not one, court papers said.

By Sept. 18, a prosecutor on the case had already “expressed her concern” about these discrepancies, police records show.

On Oct. 19, Bederow wrote a letter to the district attorney’s office citing “red flags” in the woman’s account and urging caution. Four days later, the lead prosecutor, DeGaetano, called a detective on the case, asking if he could pinpoint the defendants’ “GPS location” through their phones.

A week later, however, prosecutors decided they had enough evidence to proceed to a grand jury without the GPS records. Testing had shown a match between the men’s saliva samples and semen detected in the woman’s rape kit. The detectives were indicted Oct. 30. Hall was charged with first-degree criminal sexual act, and the top charge against Martins was first-degree rape.

When the district attorney’s office later received the phone records, they undermined the woman’s narrative. The data showed that neither man’s phone had been near where she had said they had been.

“Nothing good ever happens when a prosecutor indicts first and investigates second,” Bederow said. “Everyone loses.”

This article originally appeared in The New York Times.