“ Such opportunities will not go unused unless the courts are vigilant to protect the rights of persons who find themselves faced with such coaction of federal and state prosecuting agencies. Such vigilance becomes increasingly required as the Federal Government, through prosecuions for tax evasion, moves into the criminal areas regulated by the States. ”

“ The Federal Government sought to apprehend tax evaders. The state and federal agencies involved in this twofold investigation collaborated to obtain desired ends. Policemen suspected of taking bribes and gamblers suspected of giving them were called for questioning. Both were in jeopardy of prosecution: the police under state statute for taking bribes and under federal statute for income tax evasion; the gamblers under state statute for giving bribes and under federal statutes for income tax evasion and for failure to pay the special stamp and excise taxes levied on gambling operations. ”

“ None of these cases deals with the fruits of the compelled testimony, and defendants, like petitioners, who are forced to testify under circumstances similar to those here present, are left without the protection against self-incrimination intended by the Constitution. These cases, in my opinion, should be extended to prohibit any prosecution resulting from disclosures compelled under circumstances similar to those which exist here. But this is not an established principle and a witness is entitled to more than hopes of immunity when federal agencies seek to compel incriminatory testimony. ”