In his lawsuit, Lagrange said forensic analysis found that two paints used in the work were not invented until after Pollock died.

Experts have questioned the authenticity of at least 15 other works brought to market by Rosales over a two-decade period, according to the newspaper, adding that some collectors and dealers who purchased the pieces may have never known there were doubts about their authenticity.

A nonprofit created by Motherwell, the Dedalus Foundation, has said that seven paintings allegedly by the artist and supplied by Rosales were fakes. But there has been disagreement, with other experts arguing that some are genuine and noting that several have been shown at established art fairs.

Freedman and Weissman, speaking to the Times through their lawyers, said they still believed the works they sold were authentic and that they were not under investigation. Freedman even purchased and still owns a Motherwell, a Pollock and a Mark Rothko from Rosales for her own personal collection.

Rosales attorney Anastasios Sarikas told the newspaper that his client was indeed at the center of an inquiry by the Federal Bureau of Investigation and the United States Attorney for the Southern District of New York.

But he said Rosales "never intentionally or knowingly sold artwork she knew to be forged."

The FBI began examining the paintings in 2009, according to the Times.

Freedman resigned from Knoedler that October after a 31-year tenure, though her lawyer Ronald Spencer said the investigation had not prompted her departure.