What happens when a sexual harassment is filed to HR but there are not witnesses to verify or help the investigation? It will be her word against her supervisors’ word? What should you do in those cases??
It will depend of the investigator looking at the complaint. The outcome will be based on many factors such as previous complaints against the same person, your statements, and his/her statement. I suggest that you file it if you have not because then the employer is on notice that this particular supervisor has been accused of harassment. If it does not stop, do it again. The written trail and hopefully witnesses and the credibility of the complainant will eventually lead to disciplinary action or termination. The damages will vary if the employer failed to act on reasonable grounds from their investigations.
You may want to consult with an attorney of choice to get more information. Good luck!
My response herein is an attempt to give you general information and direction and is not intended to constitute an attorney-client relationship as perceived by state law.
If there are no witnesses, the investigator must decide which person is most credible. It is unclear from your post whether you are asking what the complainant, supervisor, or HR person should do.