D.C. Code § 47-133

On and after June 29, 1956, the Mayor of the District of Columbia is authorized in his discretion to invest and reinvest at any time in United States government securities, with the approval of the Secretary of the Treasury, any part of the general, special, or trust funds of the District of Columbia not needed to meet current expenses, to deposit the interest accruing from such investments to the credit of the fund from which the investment was made, and the Secretary of the Treasury is authorized to sell or exchange such securities for other government securities, and deposit the proceeds to the credit of the appropriate fund.