[hakfoo]

If there was actually a concern of suspicious activity, you'd think the fastest way to resolve it would be to cut out the middleman. "Your account is under investigation, call the regional FBI office and mention case number 123456 to reach the guy who filed the complaint."

This is working on the assumption that the majority of these flags end up being false positives (hence, "suspicious" activity, not "illegal"). If the common cases can be sorted out by a 30-minute phone call and faxing over some missing documentation, that saves resources on the law-enforcement side trying to reconstruct the same facts from "outside".

Of course, as you said, the real criminals will presumably take both the "bank suddenly started acting weird" and "here's an actual notice of investigation" as similarly strong signals to cut and run.