Just like in the reptile world, banks and insurance companies are faced with scams everyday. Why should they accept the fraud claim if the victim isn't willing to press charges or at the very least, make a police report? You have to file a police report for insurance claims involving theft or criminal damage in order to be reimbursed. I imagine a simple police report will very quickly cut through all the red tape at the bank. Then watch the bank go after the thief once the legal tools for them to do so are in place.
Depending upon the state, it looks like it would be a well deserved Grand Larceny charge. Even if no serious punishment is dealt out this time, having this on his criminal record will greatly increase the chance of him being justly punished for his next inevitable crime. Not to mention it will also greatly increase the chance of your in-laws being reimbursed by his parents.