The United States Supreme Court has held that the voluntary confessions of a criminally accused, made in the absence of full Miranda warnings, may be used to impeach his credibility.
Harris v. New York, 401 U.S. 222 (1971).
Janice I. Gambino,
Constitutional Law - Self-Incrimination - Use of Confessions for Impeachment Purposes,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol10/iss1/17