You are absolutely right that what you brother did MIGHT be a criminal offense. That offense might include fraud and theft, as well as violations of your state's specific power
of attorney laws. However, there are several things that stand in the way of getting the police or district attorney's office to prosecute or even investigate the matter. First of all, the prosecution would have to prove that your brother intentionally took the money and intended to keep it for himself. That would mean proving not only that he went against your father's wishes (without your father there any longer to say what his wishes were) but that he did so with the specific intent to steal the money, rather than simply as a mistake about what your father wanted and may have told him. All of this is difficult to prove unless there are written instructions from your father clearly indicating what your father's instructions were.
The question of where your father's money should go is also something that usually is handled in probate court, which is a civil proceeding. Also, as your attorney is no doubt working on, there are other, different civil proceedings available to seek the return of the money. In addition to the problems of proving a criminal case against your brother, as mentioned above, the district attorney's office is probably not interested in pursuing a criminal case for three other reasons: (1) Because these civil proceedings are available to you; (2) Because the matter involves a dispute solely among family members; and (3) Because the budgets of police departments and prosecutor offices are severely restricted these days, which often does not allow them to pursue "white collar" criminal matters such as your dispute with your brother.
Still, if your personal attorney develops evidence that clearly indicates that your brother stole this money, he or she might then ask the district attorney's office to open a criminal investigation. If the DA is willing to do so -- even just to look into the matter -- this might bring additional pressure on your brother to pay up what he owes.