D.C. Code § 34-906
For the purpose of making any investigation with regard to any public utility the Commission shall have power to appoint, by an order in writing, an agent, whose duties shall be prescribed in such order. In the discharge of his duties such agent shall have every power whatsoever of an inquisitorial nature granted in this subtitle to the Commission and shall have power to administer oaths and take depositions. The Commission may conduct any number of such investigations contemporaneously through different agents, and may delegate to such agent or agents the taking of all testimony bearing upon any investigation or hearing. The decision of the Commission shall be based upon its examination of all testimony and records. The recommendations made by such agents shall be advisory only, and shall not preclude the taking of further testimony, if the Commission so order, nor further investigation.
D.C. Code § 34-906