Apparently today is International Bystander Awareness Day so here's an old guest blog from a bystander who intervened. I always aspire to be braver than I am in these situations:
https://www.girlonthenet.com/blog/intervening-in-harassment/

@girlonthenet
I once intervened by walking up to the guy with a big scowl on my face
"Bruce ... you arsehole. You thought you could hide, but here you are. Where is our money, Bruce? Do we need to take your toes with a boltcutter to get you to pay your gambling debts?"

While My Dude was trying to explain that he was not Bruce, the girl vanished.

@screwturn jesus that’s bold

@girlonthenet
eh .. I was young, a biker, just out of the military, and would rather have liked it if My Dude had got stroppy

But the rationale was that he was going to spend ALL his mental resources on trying to clarify that he was NOT this Bruce I was hunting and clearly wanted to hurt, and that it completely sidelined the woman. She could have turned turned into a bright green mermaid and he wouldn't have noticed

If I had challenged him about her, it would have focused his attention on her

@girlonthenet
Now at nearly seventy, I would maybe be less aggressive, but might still play the crime and money angle.

Maybe more like talk on the phone, get between him and the woman and say into the phone "Hey Vito, I just found Bruce. He changed his hair and shaved of the stupid beard, but I found him. So, Bruce, we gave you 25-k, where's our product, man? Where's the STUFF?"