D.C. Code § 42-819
In case of the death of a sole mortgagee or trustee or the last survivor of several, as aforesaid, if the debt secured by the mortgage or deed of trust shall have been paid, and it is desired by the party paying the same to obtain a deed of release, the said party may file a petition in the court having probate jurisdiction, setting forth, under oath, the execution of said mortgage or deed of trust, the death of the mortgagee or trustee, the payment of the debt, and any other fact necessary to entitle the petitioner to the relief prayed, and praying for the appointment of a trustee in the place of the deceased mortgagee or trustee to execute a deed of release of said mortgage or deed of trust. It shall not be necessary to make the heirs or devises of the deceased mortgagee or trustee a party to such proceeding. The court may thereupon lay a rule upon the creditor secured by said mortgage or deed of trust, unless he shall voluntarily appear and admit the allegations of the petition, to show cause, under oath, on or before the 10th day, exclusive of Sundays and legal holidays, after the service of said rule, why the prayer of the petition should not be granted. If said party cannot be found in said District, service of said rule shall be by publication according to the practice in equity in said court. If no cause be shown, notwithstanding the service of said rule, against the prayer of the petition, the court may determine in a summary way whether said debt has been paid, and if satisfied thereof may, by decree, appoint a trustee in the place of the deceased mortgagee or trustee and invest in him the title, in law and in equity, that was in the deceased mortgagee or trustee, for the purpose of executing a deed of release as aforesaid. If matter of defense against the prayer for a release of said mortgage or deed of trust be set up in answer to said rule, the further proceedings shall be according to the practice in equity after answer filed. Nothing contained in this section shall prevent the appointment of a new trustee pursuant to § 42-814(b) and the execution of a deed of release by such new trustee.
D.C. Code § 42-819