Ethics question #132 would you drop a dime on a potential pimp killer?

Let say you know a guy “Blain” who has not seen his kid sister in 4 to 6 years. Then he moves to another city and bumps into his sister working a corner as a hooker. In a conversation with you he tells you that her pimp won’t get away with it. Three days later her pimp is found floating in the river with a round in both knees and one to the head, and Blain seems to never want to talk about the pimp or what his sister had gone through. If the cops ask for tips via an anonymous tip line would you call them on Blain as a possible suspect, or not?