Washington (CNN) Justice Department prosecutors are investigating a media leak tied to the FBI's Hillary Clinton email probe, a person familiar with the matter said, an unusually belated move that is prompting questions about political motivations since the new inquiry could involve one of the President Donald Trump's most vocal critics, James Comey.

The former FBI director in 2017 told Congress about a piece of classified evidence that played a role in his decision to unilaterally announce no charges against Clinton in a press conference that usurped the role of his superiors at the Justice Department. Before that testimony, news reports had described the classified information.

But in recent months, investigators in the Washington US Attorney's office have been looking into possible legal violations in the disclosure of that information. Investigators have interviewed witnesses about the media disclosure, according to another person familiar with the matter.

It's not clear who the target of the probe is. But Comey's role in the matter raises the prospect that prosecutors could end up examining his conduct as part of the probe.

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