Stealing manipulative boyfriend, help!!!?

My sister has been dating this guy on and off for years. She currently lives with him, receives her mail at his house, but is not on the lease. This boy is psychologically abusive. He told her the other morning to move out, take all her stuff with her, and never come back. I took her to get bags and boxes and we were back an hour later to move her out. He had locked the door to their bedroom and was carrying out bags and boxes full of all of her things, and he is holding her files, clothes, and valuables hostage until my sister agrees to make the relationship work. The police told us she had every right to be in the apartment since she is getting mail there, and he can't kick her out without going through the court. She went over there today while he was at work and broke a window to get her things out of there, but all of her things were gone. This guy will not agree to meet with her to give her her things back, he is doing everything in his power to control her and keep her from leaving, even though he treats her poorly and tells her to leave. I have tried to mediate the situation to no avail. I love my sister and I want to help her in any way I can... from a legal standpoint, is she liable for breaking and entering her own bedroom? what can be done to get her things back? she simply wants to leave an abusive relationship and he is prolonging the abuse to feel in powerful and in control. this makes me sick. i don't know what to do, and neither does she. HELP!