No, they had no legal basis to take the gun. No, they have no legal basis to keep the gun.
You need to get with an attorney here in Miami, or specifically here in Miami Beach, that can put pressure on the situation or eventually take more formal action.
Michael C. Grieco
Miami Beach, FL
This response does not establish an attorney-client relationship and is simply solicited guidance.
They should not have taken your gun. You have a permit to have the gun and could prove lawful ownership. There was absolutely no reason for them to suspect it was involved in a crime, especially since it was not reported stolen. You should look into a formal request for return of seized property as soon as possible.
Responses should not be relied upon for legal decision making. One should contact a lawyer and establish an attorney-client privilege to rely on legal advice. Any communication here is NOT considered attorney-client privilege and is not confidential.