I have been gone for awhile but I desperately need some advise and this is the only place I know to turn.You all have always have helped me when I needed it.

I have a sister who is on drugs real bad.She has almost completely abandoned her 2 daughters.She took them to my mother almost 2 years ago and left them and only now sees them once in a while.My mother has anew job now and gets paid by prepaid debit card [her pay is deposited on this card every 2 weeks].The last time my mom got paid my sister demanded that my mother give her the card so she could fill a prescription she had [pain pills] my mother refused and ended up being called all night long by the sister demanding the card.Finnally my mother stopped answering the phone and sister left a message on the answering machine saying that my mother had better leave her card in the PO box at the post office so she could get her "meds".When my sister went to the box and found it was not there she called my mother at work and jump her and that night she went and spent the night at Mom's.The other day Mom came to visit me and she had a huge bruise on her arm and when I asked where it came from she said she fell.To me it looks like finger prints where someone has either grabbed her arm real hard or something.I asked if she got any more and she told me yes in several places.I made her let me see them and it looked like someone had beat her.I tried to get her to tell me what really happened but she insists that she fell.I told her that if someone was hurting her that I would do something about it but she just started crying and said taht no one was doing anything to her,that she fell,but she wouldnt look at me when she talked.My mother isnt very old,she will just be 60 in August but she has been pretty sick the past few months.I know that my stepfather would never hurt her,they have been amrried 25 years and he absolutely adores her,so I know it wasnt him that hurt her.I beleive it was my sister and I dont know what to do.As long as Mom refuses to tell me what happened I cant legally do anything.I have thought about confronting the sister but will taht make it worse for Mom.wIll she hurt her more? I just dont know what to do! I have talked to a police officer friend and he told me that he would try to help but that as long as Mom wont talk he cant arrest her for it but that he would try to catch her out driving and pull her over and search her to see if she has any drugs.I am worried that she [ sister] will go in down there at Mom's and kill all of them sometime.What hurts me so bad is that my sister used to be the best mother,sister & daughter that anyone could ever ask for and now she is someone I dont even know.