Sorry to say it but to me your case does not seem very strong. What happened is a matter of proof. The police are probably not going ahead because they need corroboration that is non-existent.
Take care of yourself, and in the future because the boss is prone to getting physical try to never be in a situation where just you two are alone.
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I strongly disagree with the statements above. You should seek out the District Attorney of your county and go to their complaint bureau. If the police will not act., maybe the DA's office will have better understanding of the issue. Most crimes of a sexual nature do not have to have cooberation anymore. Besides your 911 call and your proof of injury is cooberation.
You may want to hire an attorney to press your case with the DA and to bring an action with the Human Rights Commission. In fact during discovery of that case you may just find the smoking gun you need to have this masher prosecuted. Look for a lawyer with experience in criminal law and employment law or civil rights law.
Good luck and do NOT give up!!
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