Former national security adviser Michael Flynn reportedly is willing to testify before the FBI and congressional committees investigating Russia’s meddling in last year’s presidential election but only if he gets immunity from prosecution.

Flynn was forced to resign from his White House post just weeks into the Trump administration because he misled Vice President Mike Pence on contacts with Russian Ambassador Sergey Kislyak.

Read: Former NSA Michael Flynn Seeking Immunity For Testimony

Flynn was caught on surveillance intercepts talking with Kislyak about the possibility of the new administration lifting sanctions against Russia. Kislyak, not Flynn, was the target of the surveillance.

The discussions occurred between the Nov. 8 election and the Jan. 20 inauguration. U.S. law prohibits private citizens from meddling in foreign policy.

A grant of immunity would prevent Flynn from being prosecuted and put him in a position to enlighten investigators on whether there was any collusion between the Trump campaign and Russian operatives, something President Donald Trump has denied.

Read: Rep. Adam Schiff Says Evidence Of Russian Collusion Is More Than Circumstantial

There are four types of immunity, according to Law.com:

  • A promise not to prosecute in exchange for information or testimony in a criminal matter,
  • For public officials to protect them from liability,
  • Sovereign immunity to protect government agencies from being sued, and
  • Diplomatic immunity to protect diplomats from being prosecuted for violating U.S. law.

Prosecutors and investigators generally offer immunity when a witness can help them prove a case. If a witness is granted immunity and then refuses to testify, the witness can be held for contempt of court and fined and/or jailed, according to Nolo.

Flynn is going for the first kind, which would protect him from a jail sentence or fine. The Wall Street Journal reported that so far, Flynn hasn’t found any takers.

The FBI has been investigating whether the Trump campaign colluded with Russian operatives since July while the Senate Intelligence Committee began taking testimony Thursday and the House Intelligence Committee investigation has stalled.