Prosecutor Joan Illuzzi-Orbon did not oppose the dismissal but added that this disclosure does not impact the strength of the remaining case.
"In short, your honor, we are moving full steam ahead", she said.
The NYPD has said it stands by the criminal case against Weinstein but has not directly addressed the alleged conduct of the investigator.
The woman who accused Weinstein of assaulting her in 2004, Lucia Evans, told the New Yorker in October 2017 that Weinstein forced her to perform oral sex on him when she was a 21-year-old college student.
Brafman said prosecutors discovered Evans' written account about her encounter with Weinstein from a fact-checker with The New Yorker, and said he would subpoena the magazine.
Why was the charge dropped?However, an email from Evans from 2015 suggests that the interaction was consensual.
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There was no immediate response from the New York Police Department.
Evans went public one year ago claiming that the Hollywood heavy hitter forced her to perform oral sex on him in his office in 2004.
Bradman accused Evans of lying to the grand jury during her testimony and called for the district attorney to look into prosecuting her for perjury.
Prosecutors said the police detective didn't share any of that information with prosecutors and urged the woman not to reveal details, saying "less is more", and that she had no obligation to co-operate with investigators.
His lawyer, Benjamin Brafman, said in court that he believes Evans lied to the grand jury about what happened. While the witness said she declined, she did not see Evans do so.
"I want to be very clear that prosecutors' decision to abandon my client's claims does not invalidate the truth of her claims", Ms Goldberg said.
The friend told prosecutors that Evans admitted she performed the sex act and during the conversation was "upset, embarrassed and shaking".
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Manhattan's district attorney dropped part of the criminal case against Weinstein on Thursday.
"Nor does it reflect on Lucia's consistent allegation that she was sexually assaulted with force by Harvey Weinstein".
The Associated Press generally does not identify people who say they are victims of sexual assault unless they consent to being identified publicly, as Evans has.
Out on $1 million bail after having entered a not-guilty plea to the first round of indictment and surrendering his passport earlier this year, Weinstein was last in court July 9 to enter another not-guilty plea.
Five charges involving alleged sex assaults on two women remain.
Weinstein is free on $1 million bail and is due back in court December 20.
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