One needn't determine who the crooks are first. If a government employee (elected, appointed, whatever) is called upon to testify about a government operation then they cannot use the 5th amendment to hide the operation of the government from the public's view. I would even assert that we should have a waiver made available to all who enter public service clarifying they will be giving up the protections against tyranny offered in the Constitution for the period of time they are employed by the tyrant.