15-yr.old female in drug abusive home, no evidence

I am a 21-year old college student residing in Indiana. I have a 15-year old sister who is living with her father in Illinois, and he is a drug abuser. Two years ago, our mother passed away and he was granted custody of my sister. Her father uses crack cocaine frequently. On several occasions, her father has become physically abusive toward my sister and other members of the household. He has choked her, punched her, and snatched her down stairs. During other abusive incidents, the police was called but they did not make a report of the fights because they had no evidence of abuse (i.e. no bruises or marks indicating harm). I am worried about the safety and mental well-being of my little sister and the othert people in the house. There are always small children around and there are four other adults in the house. The only evidence that we have against him are the people who live in the house and saw the abuse (verbal and physical) he has inflicted on my sister. Is there a way to get custody of my sister, although I have no evidence to prove that he is a drug and child abuser? Please help me!!!

If there's no evidence, there's nothing for a court to look at to determine that there is a problem. Courts act on evidence.