AceShowbiz - Nelly's alleged sexual assault victim is no longer participating in the criminal investigation into her claims because she believes the police force have botched her case.

Police in Essex, England opened an investigation last year (2018) after a woman claimed the "Hot in Herre" hitmaker masturbated in front of her and forced his penis into her mouth backstage after a concert in Southend on 5 December 5, 2017, allegations Nelly has denied, calling them "disingenuous."

In a new letter obtained by TMZ.com, the attorney for the anonymous accuser - who goes by Jane Doe - revealed that, since they've already filed a civil lawsuit over the claims, they will no longer be participating in the criminal investigation because they believe Essex Police officials have completely botched their probe.

The lawyer accused the lead detective of treating her client like a suspect instead of a victim, allegedly asking for all her phone records, including all pictures, texts, and emails between her attorney, which violates the attorney-client privilege.

Doe's legal representative also claims police officers showed up at her client's home unsolicited to try and get her to go to the station to do a follow-up interview, while it took a year for Nelly, real name Cornell Haynes Jr., to fly back to Essex to be interviewed. The attorney described the police as incompetent and accused them of being intimidated by Nelly's fame and high-powered legal team.

The 44-year-old rapper flew to Southend "on his own volition.... to work with the police in assisting their investigation to clear his name completely" in January, his representative confirmed at the time.

His legal team is currently trying to dismiss Jane Doe's civil lawsuit.

In September (2018), he settled a separate lawsuit with a U.S. woman who had accused him of rape, and he is also facing a second assault allegation from a woman who claimed he assaulted her backstage at a show in Birmingham, England in 2016.