So I was a prosecutor and this is just my opinion based on my own experience in bringing cases forward and taking them to trial. Additionally in full disclosure I never worked in a SVU unit so this is also based on second-hand knowledge based on what I’ve learned about these cases from other prosecutors who have investigated and tried them.
Sexual assault cases are IMO the hardest to win convictions on, because so many of them are “he said, she said” that come down to the credibility of the victim. In this particular case, it is undisputed that the alleged victim and Nzei had sex. The proofs apparently included the alleged victim having injuries on her face. The alleged victim says Nzei assaulted her. Nzei’s contention is that it was a consensual encounter and she asked for it to be rough. Nzei was likely going to have to testify in his own defense, and on cross examination he was going to be confronted with the fact that he gave the police a false statement, and said that he initially didn’t know/remember the alleged victim. It’s certainly possible that Nzei genuinely did not remember, but it wasn’t going to look good in front of a jury.
That said, they pushed forward with the case and indicted him on very serious sexual assault charges. The State then signed a trial memo and felt that it could win a conviction at that time. It is unusual for the State dismiss an indictment, especially as serious as this one, mere days before trial.
The only reasonable explanations that I can think of are either 1. The State found some background information about the alleged victim which undermined her credibility, or that she made the whole thing up. 2. The alleged victim came in during trial prep and recanted her story or 3. The alleged victim went AWOL shortly before trial, and the State could not reach her and thus could not proceed with the case.