D.C. Code § 23-105

(a) In a trial for an offense punishable by death, each side is entitled to twenty peremptory challenges. In a trial for an offense punishable by imprisonment for more than one year, each side is entitled to ten peremptory challenges. In all other criminal cases, each side is entitled to three peremptory challenges. If there is more than one defendant, or if a case is prosecuted both by the United States and by the District of Columbia, the court may allow additional peremptory challenges and permit them to be exercised separately or jointly, but in no event shall one side be entitled to more peremptory challenges than the other.
(b) The court may direct that jurors in addition to the regular jury be called and impaneled to sit as alternate jurors. In addition to those otherwise allowed, each side is entitled to one peremptory challenge if one or two alternate jurors are to be impaneled, to two peremptory challenges if three or four alternate jurors are to be impaneled, and to three peremptory challenges if five or six alternate jurors are to be impaneled.
(c) Any juror or alternate juror may be challenged for cause.
(d) No verdict shall be set aside for any cause which might be alleged as ground for challenge of a juror before the jury is sworn, except when the objection to the juror is that he had a bias against the defendant such as would have disqualified him, such disqualification was not known to or suspected by the defendant or his counsel before the juror was sworn, and the basis for such disqualification was the subject of examination or request for examination of the prospective jurors by or on request of the defendant.