You raise an excellent point. It's certainly possible for the notification to specify what crime is being investigated. I'd say that's an important addition,

You raise an excellent point. It's certainly possible for the notification to specify what crime is being investigated. I'd say that's an important addition, for the reasons you've alluded to. And interestingly enough I've seen things just like that. The "police" at my old college would occasionally send out emails if they were looking for a suspect. The emails would always include a brief description of the alleged crime. Perhaps they included that as a means to motivate people into reporting. I wonder if they'd have second thoughts about it if they knew some witnesses would explicitly not report anything if it was related to a crime they didn't agree with (for example, marijuana use).