Pleading the Fifth.
'Til I get home. ;-)
It wasn’t meant as an allegation. It was to show why someone should step forward when enough details have been established to move up the chain of command and file a complaint. But sometimes you need to determine the players first so you don’t tip off those who are in on something.
The government won’t pay for your defense and so even the whistleblower (or second person who was “planning” to blow the whistle) could be asked to defend why (s)he didn’t step forward “sooner”.