William "Duff" Armstrong - The Case

The Case

Armstrong was charged with the August 29, 1857 murder of James Preston Metzker in Mason County, Illinois. His father, Jack Armstrong, had been a friend of Lincoln while he was studying law in New Salem, Illinois. When Lincoln heard of the murder charge, he wrote to Jack's widow, Hannah, and volunteered his legal services pro bono. The trial was moved to Cass County and held at the courthouse at Beardstown, Illinois.

Witness Charles Allen testified that he saw Duff Armstrong strike Metzker. Under cross examination Lincoln pushed for further detail and Charles Allen testified that he was at a distance of 150 feet but could clearly see the act by the light of the full moon. Abraham Lincoln used judicial notice, then a very uncommon tactic, to show Allen lied on the stand when he claimed he had witnessed the crime in the moonlight. Lincoln produced an almanac to show that the moon on that date could not have produced enough light for the witness to see anything clearly. Based on this evidence, the jury acquitted Armstrong after only one ballot.

Armstrong went on to join the Union forces in the Civil War. He became ill in 1863 and, at his mother's request, Lincoln arranged for Armstrong's discharge. Armstrong lived long after the war; his death was reported in the New York Times on May 14, 1899.

William Duff Armstrong is buried in the New Hope Cemetery in Mason County, IL. A plaque is erected at his gravesite which reads, " WILLIAM DUFF ARMSTRONG accused slayer of Preston Metzker, May 7, 1858 freed by Lincoln in Almanac Trial".