Among the most astonishing elements of the scheme was that the painter, Mr. Qian, was able to master the styles of a diverse array of famous painters to the point that acknowledged experts and sophisticated collectors did not notice they were frauds.

The federal authorities said it was Mr. Bergantiños Diaz who recruited Mr. Qian to produce the scores of paintings and drawings that were presented as newly discovered works by major artists. They said in court papers that he treated the canvases to make them look old and that some of the proceeds from the sales were wired to bank accounts in Spain controlled by him.

In his conversation with the filmmakers, Mr. Bergantiños Diaz described how he met Mr. Qian at the Art Students League, an arts school in New York. “We knew from the school that he was very talented at doing copies of famous artists,” he told the filmmakers.

Mr. Bergantiños Diaz bought some of his works. While he insisted Ms. Rosales had the most contact with Mr. Qian, he said that sometimes they made suggestions together about what he should paint.

He said Ms. Rosales’s work with the Knoedler Gallery was independent of him, that he never met its director, Ann Freedman, and that he was not aware that Ms. Rosales was selling work made by Mr. Qian as the real thing.

“I didn’t know everything she was selling or buying because we were distanced from each other and I have my own networks,” he said, speaking sometimes through a translator.