The department, or any agent authorized in writing by it, is hereby authorized to examine the books, papers and records of any taxpayer or supposed taxpayer, and to require the production of a copy of his return as made to and filed with the Federal Government, if one was so made and filed in order to verify the accuracy of any return made, or if no return was made, to ascertain and assess the tax imposed by this article. Every such taxpayer or supposed taxpayer is hereby directed and required to give to the department or its duly authorized agent the means, facilities and opportunity for such examinations and investigations as are hereby provided and authorized. The department is hereby authorized to examine any person under oath concerning any income which was or should have been returned for taxation, and to this end may compel the production of books, papers and records and the attendance of all persons, whether as parties or witnesses, whom it believes have knowledge of such income. The procedure for such hearing or examination shall be the same as that provided by “The Fiscal Code” relating to inquisitorial powers of fiscal officers.