Summary

Portrait of William R. Day William R. Day Kepner v. United States — Opinion of the Court

Undoubtedly in those jurisdictions where a trial of one accused of crime can only be to a jury, and a verdict of acquittal or conviction must be by a jury, no legal jeopardy can attach until a jury has been called and charged with the deliverance of the accused. But, protection being against a second trial for the same offense, it is obvious that where one has been tried before a competent tribunal having jurisdiction he has been in jeopardy as much as he could have been in those tribunals where a jury is alone competent to convict or acquit.
Source: Wikisource

Portrait of William R. Day William R. Day Kepner v. United States — Opinion of the Court

But this court reversed the judgment, and in the course of the opinion it was said:
'The Constitution of the United States, in the 5th Amendment, declares, 'Nor shall any person be subject to be twice put in jeopardy of life or limb.' The prohibition is not against being twice punished, but against being twice put in jeopardy; and the accused, whether convicted or acquitted, is equally put in jeopardy at the first trial.
Source: Wikisource

Portrait of William R. Day William R. Day Kepner v. United States — Opinion of the Court

No case has been called to our attention, and after a most diligent examination of authorities, we have not been able to find a single American case where a retrial has been ordered or sanctioned by an appellate court at the instance of the prosecution, after the defendant had been once put upon his trial for an alleged felony, upon a valid indictment before a competent court and jury, and acquitted by the verdict of such jury
Source: Wikisource

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