William Duff Armstrong was born in 1833. On 29th August, 1857, Armstrong got involved in a drunken brawl in Mason County, Illinois. Armstrong struck James Metzker with a blackjack. He rode away but later fell of his horse and died.
Armstrong was charged with murder. His parents were friends of Abraham Lincoln and asked him to defend their son. Lincoln agreed and the trial began on 7th May, 1858.
The chief prosecution witness, Charles Allen, claimed that he saw Armstrong strike the fatal blow at about 11 p.m. He argued that although he was 150 feet away, he could see the event clearly as the scene was lighted by the moon overhead. Lincoln produced an almanac for the year which showed that the moon was near the horizon at that time of night.
In cross-examination, Abraham Lincoln persuaded another witness to say that he had the blackjack when the attack took place. A doctor also testified that James Metzker could have died from injuries received by falling off the horse. The jury's verdict was "not guilty". Lincoln charged no fee for his services.
On the outbreak of the American Civil War Armstrong enlisted in the 85th Illinois Volunteers. He remained in the Union Army until becoming very ill in Louisville in 1863. William Duff Armstrong died in Cass County, Illinois, in 1899.