Ex Parte Milligan
71 U.S. 2 (1866), prohibited the federal government from establishing military courts to try civilians (except where regular courts were no longer functioning in an actual theater of war). Lambdin P. Milligan had been arrested in his Indiana home in 1864 and tried in a military court on charges of aiding the Confederacy. The Supreme Court declared that neither the president nor Congress had the authority to set up such a court; Milligan, as a consequence, had been deprived of his constitutional right to trial by jury (and so was freed).
Seen and Heard
What made you want to look up Ex Parte Milligan? Please tell us where you read or heard it (including the quote, if possible).