ROOSEVELT - A Roosevelt man says a "rogue" Nassau police officer has been harassing and assaulting him for months, but police say the accuser is an admitted gang member with a violent history.Gary Mosley, 20, says he has cell phone video of officer Joseph Stacci assaulting him. He claims they have had several confrontations and that the officer has been issuing him frivolous tickets for months. The police department wouldn't permit News 12 Long Island to speak with Stacci. However, the department says that Mosley is an admitted member of the Crips street gang who has a long and violent rap sheet.Mosley denies that he is a gang member. He says police have simply labeled him as such. Mosley and his attorney have asked the department to investigate. They say the internal affairs bureau has an open case, and that they are planning to file a multimillion-dollar lawsuit against the police department next week.