I was thinking the other day about the German spies who got caught in the U.S. during World War II. They were sent to try to sabotage war production plants. At least one of them was caught, tried, and set to be executed. President Roosevelt insisted that the man be executed, as a warning and example of what would happen if this were tried again. I think this precedent is well worth considering today.
Also the railroads. I know this because for many years, my Grandfather worked undercover to catch these spies. Many more were caught than the country ever learned about.
I didn't learn about his service until I was an adult. It was that secret.
More than one. Ex Parte Quirin 317 US 1.
The eight "spies" were tried by military tribunal. Six of the eight died in the electric chair five days after the guilty verdict.