18 U.S.C. § 3596

(a) In General .— A person who has been sentenced to death pursuant to this chapter shall be committed to the custody of the Attorney General until exhaustion of the procedures for appeal of the judgment of conviction and for review of the sentence. When the sentence is to be implemented, the Attorney General shall release the person sentenced to death to the custody of a United States marshal, who shall supervise implementation of the sentence in the manner prescribed by the law of the State in which the sentence is imposed. If the law of the State does not provide for implementation of a sentence of death, the court shall designate another State, the law of which does provide for the implementation of a sentence of death, and the sentence shall be implemented in the latter State in the manner prescribed by such law. (b) Pregnant Woman .— A sentence of death shall not be carried out upon a woman while she is pregnant. (c) Mental Capacity .— A sentence of death shall not be carried out upon a person who is mentally retarded. A sentence of death shall not be carried out upon a person who, as a result of mental disability, lacks the mental capacity to understand the death penalty and why it was imposed on that person.