Thomas Caldwell, Guerrilla
The Caldwell family had migrated from Tennessee by way of Kentucky, and like a lot of young men of Southern sympathy in the border state of Missouri, young Thomas Caldwell turned to guerrilla warfare not long after the outbreak of the Civil War. Sometime in early 1862, he fell in with a guerrilla band (perhaps led by noted partisan leader Kinch West, although this is not clear), and on or about April 15 of that year, the guerrillas met a detachment of Federal soldiers and ended up killing a Captain Beard and another of the Union soldiers named Jacob Paris.
Caldwell may or may not have been the one who actually fired the shots that killed Beard and Paris, but he was evidently the only one of the guerrillas who was later captured by Federal authorities. He was charged with murder and tried, at a military commission convened in Springfield on January 24, 1863, on two specifications, one for killing Beard and one for killing Paris. He was found guilty of the charge and of both specifications and sentenced to be "shot to death with musketry."
The conviction was reviewed by President Lincoln, as such convictions often were. On August 3, 1863, he upheld the conviction and ordered that the sentence be carried out. Presumably it was, although I have found no proof of that.