Witnesses in Federal court or grand jury proceeding are provided “use” immunity, which means that none of the testimony from the witness can be used against them as evidence. So with that, they can come in and fess up to all sorts of crimes, and it cannot be used to prosecute them.
BTW, Eric Braverman, you may be aware, was put in charge of the Clinton Foundation for about a year and a half. He abruptly resigned, and many speculate that he was trying to make sure the organization conducted business legitimately, but was blocked from doing so. He disappeared for several months, but was recently provided with immunity for the third time for testimony before congress.
Here’s a good primer: