358 U.S. 74 (1958)
Petitioner was convicted and sentenced to five years imprisonment by a United States District Court in Oklahoma on a charge that he violated the Mann Act by transporting a girl from Arkansas to Oklahoma for immoral purposes.1 Over the petitioner's objection the district court permitted the government to use his wife as a witness against him.2
The wife, appearing under the name Jane Wilson, testified that she was the petitioner's wife and that she had been a prostitute both before and after the marriage.3 Before testifying she had been imprisoned as a material witness and released under a three thousand dollar bond conditioned on her appearance in court as a witness for the United States.4 The prosecutrix testified that the petitioner agreed to take her to Tulsa where she could work as a prostitute with Jane Wilson, while the petitioner denied any immoral purpose for the trip.5
The Court of Appeals for the Tenth Circuit affirmed the conviction relying on Yoder v. United States.6 Because other courts of appeals followed the rule barring a spouse from testifying against the other, the Supreme Court granted certiorari.7
The only factual issue in the case was whether the petitioner's dominant purpose in making the trip was to facilitate the practice of prostitution in Tulsa.8
Whether the common-law rule barring one spouse from testifying against the other in a federal criminal prosecution should be modified to permit voluntary adverse testimony by the spouse?9
The common-law rule bars one spouse from testifying against the other in federal criminal cases to foster family peace and harmony for the benefit of the public as well as the spouses and children.10 Federal courts may interpret the common law in light of reason and experience under Federal Rule of Criminal Procedure 26.11 The rule should not be modified to distinguish between compelled and voluntary testimony because both forms of adverse testimony are likely to destroy marriages and the distinction lacks support in precedent or policy.12
No. The established facts show that the petitioner was convicted and sentenced to five years imprisonment.13 The district court permitted his wife to testify over objection in a Mann Act prosecution for transporting a girl from Arkansas to Oklahoma for immoral purposes.14 The rule rests on the belief that pitting spouse against spouse in a criminal trial where life or liberty is at stake would engender bitterness and destroy family harmony.15 The facts here illustrate the point because the wife testified that she was a prostitute both before and after the marriage on a sharply contested issue of the petitioner's dominant purpose for the trip.16
Reason and experience do not support abandoning the rule, as most American states retain it with only limited exceptions and Congress has made only narrow statutory modifications rather than wholesale change.17
The common-law rule barring one spouse from testifying against the other should not be modified to permit voluntary adverse testimony by the spouse.18
Related opinions on this issue
Justice Stewart concurred in the judgment.19 He emphasized that the rule originated from long-rejected concepts that a criminal defendant was incompetent to testify and that husband and wife were one person in law.20 Any rule impeding the discovery of truth deserves the most careful scrutiny under reason and experience rather than mere assumptions about domestic tranquillity.21
He agreed that the present record did not present an appropriate vehicle for modification because the wife had been imprisoned as a material witness and released under a three-thousand-dollar bond conditioned on her appearance.22 These circumstances are inconsistent with truly voluntary testimony and likely to make voluntariness difficult to administer in future cases.23
Whether the admission of the wife's testimony against the petitioner was harmless error?24
Under Federal Rule of Criminal Procedure 52(a), an error in admitting evidence is harmless only if it does not have substantial influence on the jury, as set forth in Kotteakos v. United States.25
No. The established facts show that the only factual issue was whether the petitioner's dominant purpose in making the interstate trip was to facilitate prostitution in Tulsa.26 This issue the jury could have resolved either way depending on whether it believed the prosecutrix or the petitioner.27 The wife's testimony that she was the petitioner's wife and had been a prostitute both before and after the marriage was added to the mere presence of a wife testifying against her husband.28 This created a strong suggestion to the jury that the petitioner was the kind of man to whom such an immoral purpose would have been natural.29
It was likely tipping the scales on the close question of motivation.30
The admission of the wife's testimony against the petitioner was not harmless error.31