Possible serious crime that I think needs to be reported.

This is a very iffy situation and I don't want to give too much at this time but also think something needs to happen quickly to prevent any future events.

I have a friend that is scared for her life to report anything that her ex did in the past. All of them being very intense crimes mostly abuse physical, mental, financial really all of the above. I'm certain this could be corroborated with others as well. My friend and the man share a child together and she fears for her child as well. He seems to be mentally unstable and there is a family records (his dad) of severe crimes. Dad was charged with manslaughter only because of temporary insanity. He's free now. My friend is thinking that he has potentially committed similar crime to a certain group of women. This was back in 2019. She suspects this because he told few details of the event and that he got enraged with this woman and that he started hitting her. My friend has brought up how she was worried about the girl and how he said he's never going to get caught for what he did to her. The only thing being known for certain was that he beat her. He never confessed to more to her but she suspects much more. She mentioned she was at house party and a girl that he had associated with before came up to her and told her that he had came into the gas station she was working at with no shoes or socks on and had blood on his clothes. She mentioned he had a wad of cash that he used some gas stations slip on slides. This gas station is on the way back to his house from where the suspected crimes happened.

My friend cannot remember who the girl was that told her about what she saw that night in the gas station but she knows what gas station it was and the year it most likely happened. She has a list of possible cars he drove. Based off the reported clothes he was wearing she believes that it was comfortable temperature for someone to be wearing shorts. Especially to the city that he went to. Would've been chilly in early October in that city in the state we live in. She mentioned he had got a hotel up there for the activities and that where he at least beat her.

She fears for her daughter and her future around this man. She fears for herself and her future having to co parent with this type of person. She's fears for future victims.

In my own experience with this guy I do see the signs of unstable mental health undoubtedly. I have known him since I was at least 15. I don't know him well because he was not a great person then either. The last few years he has admitted to drug use mostly because it has landed him in hospital but all things that a child should never be exposed to and also not anything that really helps keep a healthy mental state.

I'm writing this because I think something should be done but she deeply fears for herself if all this gets stirred up because he'll know it was her who reported unless he's just telling everybody that he's soliciting sex and beating women if not more. The more is only speculation but based off strong feelings and own experience of abuse she endured while they were together.

For my own paranoid thoughts on this subject,

This is a fictional story

So in this story what should my friend or my own fiction character do?