26 CFR § 20.6018-4 - Returns; documents to accompany the return.
(a) A certified copy of the will, if the decedent died testate, must be submitted with the return, together with copies of such other documents as are required in Form 706 and in the applicable sections of these regulations. There may also be filed copies of any documents which the executor may desire to submit in explanation of the return.
(b) In the case of an estate of a nonresident citizen, the executor shall also file the following documents with the return:
(1) A copy of any inventory of property and schedule of liabilities, claims against the estate and expenses of administration filed with the foreign court of probate jurisdiction, certified by a proper official of the court; and
(2) A copy of any return filed under any applicable foreign inheritance, estate, legacy, or succession tax act, certified by a proper official of the foreign tax department.
(c) In the case of an estate of a nonresident not a citizen of the United States, the executor must also file with the return, but only if deductions are claimed or the transfer of the estate is subject to the tax imposed by section 2107(a) (relating to expatriation to avoid tax), a copy of the inventory of property filed under the foreign death duty act; or, if no such inventory was filed, a certified copy of the inventory filed with the foreign court of probate jurisdiction.
(d) For every policy of life insurance listed on the return, the executor must procure a statement, on Form 712, by the company issuing the policy and file it with the return.
(e) If, pursuant to section 2032, the executor elects to have the estate valued at a date or dates subsequent to the time of the decedent's death, the executor shall file with the return evidence in support of any statements made by him in the return as to distributions, sales, exchanges, or other dispositions of property during the 6 month (1 year, if the decedent died on or before December 31, 1970) period which followed the decedent's death. If the court having jurisdiction over the estate makes an order or decree of distribution during that period, a certified copy thereof must be submitted as part of the evidence. The district director, or the director of a service center, may require the submission of such additional evidence as is deemed necessary.
(f) In any case where a transfer, by trust or otherwise, was made by a written instrument, a copy thereof shall be filed with the return if (1) the property is included in the gross estate, or (2) the executor pursuant to the provisions of paragraph (c)(7) of § 20.6018–3 has made a disclosure of the transfer on the return but has not included its value in the gross estate in the belief that it is not so includible. If the written instrument is of public record, the copy shall be certified, or if it is not of record, the copy shall be verified. If the decedent was a nonresident, not a citizen at the time of his death, the copy may be either certified or verified.
(g) If the executor contends that the value of property transferred by the decedent within a period of three years ending with the date of the decedent's death should not be included in the gross estate because he considers that the transfer was not made in contemplation of death, he shall file with the return (1) a copy of the death certificate, and (2) a statement, continuing a declaration that it is made under the penalties of perjury, of all the material facts and circumstances, including those directly or indirectly indicating the decedent's motive in making the transfer and his mental and physical condition at that time. However, this data need not be furnished with respect to transfers of less than $1,000 in value unless requested by the district director.