Double Jeopardy, in law, being subjected twice to prosecution or punishment for the same offense. The Fifth Amendment of the U.S. Constitution prohibits this practice: “nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb.” This clause is interpreted to cover all criminal prosecutions. There are certain situations in which being tried twice is not considered double jeopardy—for example, as the result of a mistrial. Under a 1969 ruling by the U.S. Supreme Court, the states, as well as the federal government, must offer protection against double jeopardy.
It's possible that an MRI lie detector could detect truthfulness more accurately than a polygraph machine. How would it work?
If you need an analogy for PRISM, one apt comparison would be to HBO's show "The Wire." Just swap "U.S. government" for Baltimore police, "Internet data" for phone wiretaps, and name the target as "really anyone" instead of drug traffickers. Got it?