My sister is having problems with her husband. He is abusing her and doesn't allow her to leave him

Hi.  My sister is haveing problems with here hasbund, hi is threating here if she leaves here, he will go after here with all he have.  She aslo hase some abuse photos thet he abuse on here. Aloso she make a vidoe that he sead to here mom thet he wans to heard here,and take his kid and live. I sead to here u have to go to police, but she is aferad.