Image Justice Sylvia G. Ash faces federal obstruction of justice charges related to corruption at the Municipal Credit Union.

When the former chief executive of the Municipal Credit Union pleaded guilty last year to stealing nearly $10 million from the 500,000-member financial institution, federal prosecutors said he had gone to some lengths to hide his long-running embezzlement scheme.

The chief executive, Kam Wong, “tried to cover up what he had done by making false statements to federal investigators and creating false and misleading documents,” the prosecutors said.

On Friday, federal prosecutors said that Mr. Wong had been helped in the cover-up by a high-ranking ally: a Brooklyn judge who led the credit union’s board of directors.

The judge, Justice Sylvia G. Ash of State Supreme Court, was arrested after arriving at La Guardia Airport from Miami. She was charged in a criminal complaint with trying to thwart the federal inquiry into Mr. Wong’s theft in several ways.