The investigation will remain open until a determination is made under § 103.400, or a conciliation agreement is executed and approved under § 103.310. Unless it is impracticable to do so, the Assistant Secretary will complete the investigation of the alleged discriminatory housing practice within 100 days of the filing of the complaint (or where the Assistant Secretary reactivates the complaint, within 100 days after service of the notice of reactivation under § 103.115). If the Assistant Secretary is unable to complete the investigation within the 100-day period, HUD will notify the aggrieved person and the respondent, by mail, of the reasons for the delay.