42 U.S. Code § 3757 - Interest-bearing trust funds
A State or unit of local government shall establish a trust fund in which to deposit amounts received under this part.
Each amount received under this part (including interest on such amount) shall be expended before the date on which the grant period expires.
A State or unit of local government that fails to expend an entire amount (including interest on such amount) as required by paragraph (1) shall repay the unexpended portion to the Attorney General not later than 3 months after the date on which the grant period expires.
Amounts received as repayments under this section shall be subject to section 3712g of this title as if such amounts had not been granted and repaid. Such amounts shall be deposited in the Treasury in a dedicated fund for use by the Attorney General to carry out this part. Such funds are hereby made available to carry out this part.