1. When a prosecutor offers a lesser sentence or no charges in exchange for testimony, he has suborned perjury and should be jailed.
We must get back to the notion that to commit a crime, one must know of the law and one must intend to commit an act that breaks it. That concept is no different than the criteria used for an insanity plea.
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Ignorantia juris non excusat
(Latin for "ignorance of the law does not excuse" or "ignorance of the law excuses no one") is a legal principle holding that a person who is unaware of a law may not escape liability for violating that law merely because he or she was unaware of its content. ...- wiki