When a consent to search has been given by a person in custody, is that consent valid?

When the claimed consent has been given by a person in custody it is appropriate to be "particularly sensitive to the heightened possibilities for coercion," see id. at 240 n.29, 93 S.Ct. 2055; but the fact of custody alone does not mean that a consent to search was coerced, United States v. Watson, 423 U.S. 411, 424-25, 96 S.Ct. 820, 828, 46 L.Ed.2d 598 (1976). Where there is no indication that the subject was "unable in the face of a custodial arrest to exercise a free choice," a valid consent may be given. Id. at 425, 96 S.Ct. at 828.