The taxes imposed by this chapter shall be assessed within three years from the date on which such taxes became due and payable. In the case of a false or fraudulent return with intent to evade payment of the taxes imposed by this chapter, or a failure to file a return, the taxes may be assessed, or a proceeding in court for the collection of such taxes may be begun without assessment, at any time. The Commissioner shall not examine any person’s records beyond the three-year period of limitations unless he has reasonable evidence of fraud or reasonable cause to believe that such person was required by law to file a return and failed to do so.