D.C. Code § 49-103
When there is in the District of Columbia a tumult, riot, mob, or a body of men acting together by force with attempt to commit a felony or to offer violence to persons or property, or by force or violence to break and resist the laws, or when such tumult, riot, or mob is threatened, it shall be lawful for the Mayor of the District of Columbia, or for the United States Marshal for the District of Columbia, or for the National Capital Service Director, to call on the Commander-in-Chief to aid them in suppressing such violence and enforcing the laws; the Commander-in-Chief shall thereupon order out so much and such portion of the militia as he may deem necessary to suppress the same, and no member thereof who shall be thus ordered out by proper authority for any such duty shall be liable to civil or criminal prosecution for any act done in the discharge of his military duty.
D.C. Code § 49-103