How a scandalous murder trial changed American law forever

History · Published 8 October 2026 Swipe more like this →

In short: In 1859, a prominent Congressman shot his friend dead in broad daylight near the White House. The motive was a sordid affair, but the legal defense was something entirely new: a plea of temporary insanity that would leave a lasting mark on the American courtroom.

The trial of Daniel Sickles in Washington, D.C., was a sensation that captivated the mid-19th-century press. Sickles, a 39-year-old Congressman from New York known for his hair-trigger temper, was accused of murdering Philip Barton Key. On a Sunday afternoon, the murder took place on the Lafayette Park pavement, situated near the White House such that the President might have seen it from his front windows. The incident occurred on a Sunday afternoon on the sidewalk. This public killing happened so close to the White House that it could have been observed from the President's windows.

The victim, Key, was a man of significant social standing and the son of Francis Scott Key, the author of 'The Star Spangled Banner'. He was also a close friend of Sickles, whose political influence with President James Buchanan had helped secure Key's appointment as Washington's district attorney. The motive for the shooting was an adulterous affair between Key and Sickles' wife, the 22-year-old Teresa Sickles.

The legal proceedings, held from April 4 to April 26, 1859, became a national spectacle. The defense team, which included Edwin M. Stanton, employed a groundbreaking strategy: the first use of a plea of temporary insanity in a United States court. They also appealed to the 'unwritten law' to justify the homicide. The jury returned a verdict of not guilty, a decision that was significant for its legal precedent, even as it caused irreparable damage to Sickles' career as a leader in the Democratic Party. The trial's dramatic nature was heightened by the presence of glamorous celebrities and spellbinding lawyers. This sensational event was fueled by political intrigue and a plot reminiscent of an Italian opera.

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