What Do I Do?

So here’s some vague background knowledge to the issue.

This couple I went to high school with broke up for a bit because the girl found out that her boyfriend had cheated on her at the party that she organized for him through the phone that she bought him. The most pressing part is that he (19M) cheated on her with a minor (15F). The issue is that my best friend (who I was telling about all of this) dates one of my old friends from highschool who basically share a very close tight knit friend group with this guy.

My bff’s boyfriend asked her if it was alright for their friend group to essentially have a conversation with him and cut ties off with him considering what he did was very disgusting. Initially I thought it was a bad idea because the information was fed through a line of the guys best friends on campus to one of their girlfriends who is a great friend of mine who then told me and so forth. I was against it because we could potentially lose the string of information to be able to build a report to the police.

As I have been thinking, I have been second guessing my decision. However, if they cut off ties with him then he’ll wonder who told them as he had initially only told one person that then went down the line.

My question is what do I do here?