7:30 AM PT -- The judge released a letter from the D.A.'s office to Weinstein's lawyer, which says in part the witness in question said, among other things, Weinstein offered to give Evans cash if she exposed her breasts to him and that Evans told her Weinstein promised her an acting job in return for oral sex. The upshot -- the witness says Evans was not forced to perform oral sex.

According to the letter, the detective told the witness she had no obligation to cooperate with prosecutors and "less is more."

Harvey Weinstein just scored a huge victory in his sexual assault criminal case ... a judge just threw out one of the 3 cases in which he was charged.

The judge said the case involving then-actress Lucia Evans was dismissed ... this after prosecutors jumped the gun and asked the judge to 86 the charge of sexual assault.

TMZ broke the story ... the lead detective in the Weinstein cases is under investigation after allegedly tampering with a witness who claimed Evans admitted to her she voluntarily engaged in oral sex to score an acting role. Evans claims Weinstein forced himself on her, but the witness says otherwise.

The detective allegedly hid information about the witness in dealing with prosecutors and allegedly cajoled the witness into not disclosing what she knew.

Weinstein's lawyer, Ben Brafman, asked the judge to review all of the detective's work on the case. The judge did not say whether he'll do that.

There are still 5 criminal charges against Weinstein involving 2 other women.

Originally published 7:04 AM PT