Sometimes the employ feels betrayed by being accused or the finger pointed at them.  If a person is guilty they could try to cause enough of a scene so that it will take the attention and resources away from what they have done.  They may also simply quit to try and remain their innocence.  It's important that the organization follow all rules and policies that are in place.  If someone knows that they could be prosecuted to the full extent of the law and that they will be punished they will be less likely to commit fraud.  A victim's anger may deflect from the investigation, they may forget details and they may confront the person who committed the fraud, in turn destroying the investigation.