Other Important Issues
Don't delay. You should contact an attorney as soon as practical. The DOJ and state reward programs have a statute of limitations that is either six or ten years (depending on certain factors). The IRS program has a three year limitation, unless you have clear and convincing evidence of intent to defraud and then there is no statute of limitations. In addition, these programs only allow the first to submit an application to receive a reward.
Don't talk too much. Don't discuss your fraud allegations with anyone except your attorney. Only one person receives a reward for each fraud case, and you risk someone else using your information to file a claim if you talk too much about it to others.