The 2012 U.S. Fraud Examiners Manual spells out guidance for corrective action. It notes that policies with consequences and processes for people who commit or condone fraudulent activity are an important deterrent for fraud. Possible consequences include termination of employment, reporting the incident to law enforcement or regulatory authorities and pursuit of civil or criminal action against the perpetrators.
Of course, legal counsel should be consulted before taking action. But putting policies in place and notifying employees of potential actions the company might take can be a good deterrent. In addition, the policy should include a requirement to fix any control weaknesses that allowed the fraudulent activity to occur.