A person granted immunity gives up his or her Fifth Amendment right against self-incrimination and must answer all questions. For a prosecutor who waives the opportunity to charge a particular witness, the trade-off presumably is information that leads to a case against someone suspected of a more serious crime. Lewinsky could be subject to perjury charges if she lied when she signed an affidavit in the Paula Jones case. There are reports that she denied having a sexual relationship with Clinton in that affidavit. If people urged Lewinsky or Tripp to lie in their affidavits, those people could be charged with subornation of perjury.
Subornation of perjury occurs when someone asks another person to lie while under oath.
To prove this charge, a prosecutor would have to show both that an individual knowingly lied under oath and that the perjured statement was sought by the accused person.