Just looking for some advice from people familiar with this kind of stuff. Im not sure where on Reddit to ask.

Long story short, I am aware of a situation where a man is deliberately seeking out young, vulnerable, mentally ill, psychologically damaged women (often with conditions like PTSD and BPD), to use dark psychology tactics on. Specifically those taught by various pick-up artists, redpill gurus, etc., and he's specifically using the most unethical ones. He was clearly using these on his ex-girlfriend, and continues to do so. I don't know these women, but I know who some of them are. I know him, but don't want to blow my cover. The man also has a history of what is legally considered sexual assault. Supposedly taught by pick-up artists. I don't believe these women are aware. He doesnt have much luck with women, he's an incel anyhow.

What would be the best course of action for me to take here? I'm in a different country. The people of concern are in the UK.