Missappropriation of Funds

Over the past 36 months I have been trying to recoup $97,000 that was misappropriated from my brokerage account. I do not have the funds to go through a long Arbitration or Civil case as they will cost between $25-50,000. I have been blown off by the SEC, NASD and other regulators. Who could I contact to press criminal charges against the broker and firm. I have been told that the prosecuters will not represent individuals and will only pursue a case if it can be proven that the conduct is affecting a large number of people or an industry. What are my options as an individual, and why will the authorities not prosecute people that missappropriate funds in a brokerage account, but they will prosecute people that walk into a bank and take money. To me there is no difference. Could someone please help me understand??