There is an irony to the decision of the Obama administration to try Khalid Sheikh Mohammed and four other co-conspirators in a civilian court. Have you ever heard President Obama compared to Abraham Lincoln? You've heard the whole "both are skinny lawyers from Illinois who reached the White House with slender resumes" line?
Well, John Wilkes Booth and the others involved in Lincoln's assassination were tried by a military tribunal, even though the crime occurred in the United States and in the absence of a formal declaration of war. Or ANY war, for that matter, as the Civil War had ended a few days prior to the slaying.
The law school of the University of Missouri at Kansas City has significant details on its Famous Trials website:
"Secretary of War Edwin Stanton favored a quick military trial and execution. According to Secretary of Navy Gideon Welles, who favored trial in a civilian court, Stanton "said it was intention that the criminals should be tried and executed before President Lincoln was buried." (Lincoln was buried on May 4, before the start of the conspiracy trial.) Edward Bates, Lincoln's former attorney general, was among those objecting to a military trial, believing such an approach to be unconstitutional. Understanding the use of a military commission to try civilians to be controversial, President Johnson requested Attorney General James Speed to prepare an opinion on the legality of such a trial. Not surprisingly, Speed concluded in his opinion that use of a military court would be proper. Speed reasoned that an attack on the commander-in-chief before the full cessation of the rebellion constituted an act of war against the United States, making the War Department the appropriate body to control the proceedings."