The former Bronx assemblyman who worked as an undercover informant to ferret out legislative corruption in Albany pleaded guilty Tuesday in federal court in Manhattan to lying to prosecution agents about media interviews he gave.

Nelson Castro, 41, a key figure in the corruption case against sitting Assemb. Eric Stevenson (D-Bronx), faces up to five years in prison, but despite new questions about his credibility he was allowed to keep a plea deal that would call for leniency if he tells the truth in the future.

Michael Farkas, Castro's lawyer, said that although questions about media interviews were tangential to the corruption case, "The government obviously takes very seriously deceit in any form, no matter the degree to which that deceit relates to a matter."

Castro became an informant while serving as an assemblyman in 2009 after he was implicated in a Bronx election-fraud perjury case.

His unusual double life as a snitch and a sitting legislator made him a symbol of the extent of Albany corruption amid a spate of cases this spring after his cooperation led to the April indictment of colleague Stevenson and four others in a bribery case involving day care centers.

In May, he gave an interview to a Spanish language Web-based production. But in June, he admitted Tuesday, he lied about having given the interview when asked about it during a session with federal investigators preparing the case.

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"I falsely stated to those same investigators that I had earlier failed to disclose my participation in the May 2013 interview because I did not remember it," Castro said during his plea. "Finally, I also falsely stated . . . that I had not discussed my cooperation with law enforcement investigations during the May 2013 interview."

Law enforcement officials typically frown on interviews from their witnesses because they can provide fuel for cross-examination, but Farkas said the media interview did not itself violate the initial plea agreement with prosecutors. Castro's new agreement prohibits discussing his case with outsiders.

In addition to Tuesday's plea, Castro -- who resigned from the Assembly after his cooperation became public -- also has agreed to plead guilty in a state court case in the Bronx that accuses him of lying about election petitions he filed.