When Lincoln heard of the murder charge, he wrote to Jack's widow, Hannah, and volunteered his legal services pro bono.
I am anxious that he should be given a fair trial at any rate; and gratitude for your long-continued kindness to me in adverse circumstances prompts me to offer my humble services gratuitously in his behalf.
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 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.
A story arose many years later that Lincoln had modified the almanac, but this was refuted by Abram Bergen, who had witnessed the trial as a young attorney, and later served as a justice of the New Mexico territorial supreme court.
A small informational 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".