The director of National Intelligence could be investigated for perjury, following news Tuesday that he gave false information to Congress in March.

The DNI published a letter on its website Tuesday that Director James Clapper sent to the chair of the Senate Intelligence Committee. He admitted to giving "clearly erroneous" testimony before the committee in March when asked specifically whether an NSA program existed that monitored hundreds of millions of Americans. He answered "No."

One expert says these kinds of situations involve some gray area.

"If you testify under oath before Congress and lie, you're at risk for being prosecuted for perjury," says Cary Feldman, who served as a lawyer in the Office of Independent Counsel in the late 1990s. "But that doesn't happen often."

[READ: National Intelligence Director Apologizes for Lying to Congress]

Feldman contributed to the investigation of then U.S. Interior Secretary Bruce Babbitt, who was suspected in 1998 of lying to Congress about reportedly receiving political donations in exchange for denying an Indian casino license. Babbitt was eventually cleared of any wrongdoing.

Clapper explained he was confused by the question posed by Sen. Ron Wyden, D-Ore., regarding "dossiers on millions of Americans." The director said in the letter that he also did not want to release classified information about a then-classified program.

The existence of government metadata collection has since been declassified, following reported leaks from Edward Snowden regarding an NSA program known as PRISM.

"To commit perjury, you have to do it willfully, which means knowingly or intentionally," says Feldman, now an attorney with law firm Feldesman Tucker Leifer Fidell. "[Clapper] is caught between either lying to Congress or revealing directly or indirectly classified information. It's a tough spot."

[ALSO: Clapper Says NSA Taps Authorized Only for 'Reasonable Suspicion']

Feldman points to the nuances of open sessions like the March 12 hearing. Clapper was asked whether a classified program exists. If he had followed procedure and declined to answer, opting instead to continue in a private or executive session, he all but infers the program exists and risks revealing classified information by implication.

Those with top-level security clearances also face consequences for releasing this kind of information.

Feldman says the likelihood of an investigation depends on whether enough members of Congress believe that Clapper willingly mislead them.

"It seems to me he is certainly subject to an investigation if someone wants to investigate, because he gave a material statement under oath that he admits was erroneous. That's most of the elements of perjury right there," says Feldman. "What his intentions were – since a truthful answer would have required him to reveal classified information – is the difficult part."

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