On April 14, 1865, Abraham Lincoln was murdered by John Wilkes Booth, and Secretary of State William H. Seward was brutally stabbed. Clearly a conspiracy was afoot. Judge Advocate General Joseph Holt was put in charge of the investigation and trial. He first set out to punish all of Booth's accomplices and then wanted to go after Jefferson Davis, whom he felt had instigated the assassination-despite stern opposition, not least of all from Lincoln's...