The two-witness rule is fine for settling issues of sin or immorality that do not rise to the level of criminal actions. The problem with the two-witness rule is when it is applied in cases where there are crimes involved. Police need to be contacted, period. Their investigation and possible trial/conviction of a person is separate from the 'spiritual' investigation the elders are supposed to perform. There's no reason to prevent a person from going to the authorities or even advising against it when the law has been broken.
They should also butt out of any sort of civil legal action taken by members of the congregation. If a brother ripped you off, a group of elders is probably not qualified to perform a proper investigation and would lack legal authority to do things like subpoena documents or personal records (phone/email/etc). Telling you to let it go because it might make the organization look bad is ridiculous and stupid. It also protects scammers who might realize that a JW congregation is a perfect place to con a bunch of people out of their money (a scenario that has happened before, from what I've been told).