Ex Parte Milligan
United States Supreme Court
71 U.S. (4 Wall.) 2 (1866)
In 1863, Congress authorized President Lincoln to suspend habeas corpus subject to certain conditions, including a requirement that officials give federal judges lists of detained citizens so that anyone not indicted by a grand jury could seek release. Lambdin Milligan (defendant), an Indiana civilian with no military background, was arrested in October 1864, tried before a military tribunal, convicted of conspiracy against the government, and sentenced to death. In January 1865, a federal grand jury for Indiana declined to indict Milligan, satisfying one condition of the 1863 statute; Milligan then petitioned for release, arguing the military tribunal had no jurisdiction to try him while Indiana's civilian courts remained open.
Whether a military tribunal has jurisdiction to try and sentence a civilian for conspiracy where the civilian courts of the relevant state remain open and functioning.