Peter Conover Hains Jr. (January 9, 1872 – February 5, 1955) was a United States Army captain convicted of killing his wife's lover.

The crime, known as the Hains-Annis Case or the "Murder at the Regatta," played an important role in the development of criminal and matrimonial law.

The murder, committed while Hains was still an active duty Army officer, did not disqualify him from military service; after he had been convicted and incarcerated, following the passage of a Congressional act which would have allowed the dismissal of convicted service members, Hains resigned from the United States Army in 1911.

[3] It was one of the last cases in which a defendant pleaded Dementia Americana, the psychiatric pathology that allegedly drove American men to kill the lovers of their unfaithful wives.

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