D.C. Code § 22-4508
No seller shall within the District of Columbia deliver a firearm to the purchaser thereof until 10 days shall have elapsed from the date of the purchase thereof, except in the case of sales to marshals, sheriffs, prison or jail wardens or their deputies, policemen, or other duly appointed law enforcement officers, and, when delivered, said firearm shall be transported in accordance with § 22-4504.02. At the time of purchase, the purchaser shall sign in duplicate and deliver to the seller a statement containing his or her full name, address, occupation, date and place of birth, the date of purchase, the caliber, make, model, and manufacturer's number of the firearm and a statement that the purchaser is not forbidden by § 22-4503 to possess a firearm. The seller shall, within 6 hours after purchase, sign and attach his or her address and deliver one copy to such person or persons as the Chief of Police of the District of Columbia may designate, and shall retain the other copy for 6 years. No machine gun, sawed-off shotgun, or blackjack shall be sold to any person other than the persons designated in § 22-4514 as entitled to possess the same, and then only after permission to make such sale has been obtained from the Chief of Police of the District of Columbia. This section shall not apply to sales at wholesale to licensed dealers.
D.C. Code § 22-4508