What is garrity law?

Answer 1

The Garrity Rule is a court decision, not a statute. It says that when government employers investigate employee conduct that may be criminal, the employer cannot compel the accused to answer questions by threatening discharge. That compulsion violates the 5th Amendment.

Employers investigating likely criminal conduct can promise the accused that their answers will not be used in any criminal prosecution of them. Then the accused must answer or be discharged, even if the answer would subject them to civil penalties, discipline, or the criminal conviction of a friend.