Reporting statutory rape

I want to report my ex husbands niece for being with an 19 year old when she is only 14. Nobody seems to care (her parents) and I am completely disgusted. 
Update- we live in MN so it is illegal. I would mind my own business but she was my niece since birth until recently. She disclosed sexual abuse by an uncle that her mother didn't report and when law enforcement got involved she took back her story. FYI the divorce happened due to inappropriate sexual action of my ex in front of my children and they are court ordered no contact with this side of the family. It breaks my heart to see my niece in this situation. No ill intentions :(  this man is graduated high school and she is just entering 9h grade this year.