It leaves Weinstein facing allegations largely related to two women, but Brafman argued that Evans' "perjury" also taints the first count against Weinstein, if not the entire case.
"People always ask why don't sexual assault survivors come forward, this is why", she said.
Prosecutors said actress Lucia Evans had given a witness a different version of the alleged sex assault from the one she had given them.
The woman also told the detective - identified by Weinstein's lawyer as Nicholas DiGaudio - that sometime after Evans' office meeting with Weinstein, she suggested what happened was consensual, according to the letter. The five remaining charges include predatory sexual assault, criminal sexual act in the first degree, rape in the first degree and rape in the third degree.
Manhattan District Attorney Cyrus R. Vance Jr. has already been fiercely criticized for declining to prosecute Weinstein when an Italian model accused him of grabbing her breasts in 2015.
Weinstein appeared before New York Judge James Burke as his lawyers tried to have some or all of the charges he faces dismissed. Evans claimed that Weinstein promised an acting role if she gave him oral sex.
The witness had given the different account to a NY police officer who had failed to tell prosecutors, the letter added.
Weinstein's lawyer Benjamin Brafman maintained the jettisoned count is a sign the entire case is built on a weak foundation, one he and the legal team intend to spend the next several weeks undermining. He also said he believed a police detective had corruptly attempted to influence the case by keeping the witness from testifying about her misstatements. While the witness said she declined, she did not see Evans do so.
"The integrity of these proceedings has been compromised", he claimed.
"Nor does it reflect on Lucia's consistent allegation that she was sexually assaulted with force by Harvey Weinstein".
The 66-year-old father of five, out on a $1 million bail and forced to wear a Global Positioning System monitor, has long pleaded not guilty to six counts allegedly committed against three women in 2004, 2006 and 2013.
Weinstein appeared in Manhattan Criminal Court on Thursday morning as Judge James Burke made a decision to dismiss count six of the eight-count indictment against the 66-year-old film producer.
The movie mogul's fabled career imploded after he was hit by a tidal wave of lurid allegations relating to the rape and sexual of a large number of women. He has pleaded not guilty and is free on US$1 million bail.
Assistant District Attorney Joan Illuzzi-Orbon, the lead prosecutor in the case, insisted that the agreement to drop the count would have no bearing on the case's resolution. "The evidence shows that the criminal case against him is strong".
New York Police officials poured on the pressure, too, saying publicly they believed they had gathered ample evidence to make an arrest.