Out of state Constant threats, invading privacy, stalking and etc?

I have a question about a friend who is sufferin under being hared, threatening, mocked, bullied, invading any privacy of her life and family. The person is a wife of her son's father who lives out of state. Constantly tellin her she hope the child dies, he's only 4. Laughs in the face to my friend. Finds every information about her family and friends and threatens so many way u cant even imagine. Knows where she lives even it's unpublish. This woman has 2 kids from this man and is so jealous that my friend has his child. She and her husband hates the child and doenst want nothing to do with him but constantly puts my friend in misery. Even she is blocked or my friend creats another sn or email. she found her way back to her even there is no infomation about her. Police wont do anything. What is it that she is doing and what can be done to stop this????