Immunity from prosecution may be granted by Commissioner when applicant cooperates and fully discloses income, subject to withdrawal for concealment. A person whose settlement proceedings have abated may apply to the Principal Commissioner or Commissioner for immunity from prosecution before prosecution is instituted; the Commissioner may grant conditional immunity if the person cooperates after abatement and makes a full and true disclosure of income and its sources, but immunity may be withdrawn for non compliance or if the person concealed material particulars or gave false evidence, after which prosecution may proceed.