An Italian prosecutor said such cooperation had not improved since the Sept. 11 attacks.
Italian prosecutors said there was nothing on it.
Italian prosecutors charge that some works purchased by the Fleischmans came from illicit sources.
Italian prosecutors have made several arrests in the case, and more developments are sure to come.
But the biggest change has come from the informants, whose numbers continue to grow as Italian prosecutors keep up pressure against organized crime.
Italy is holding him while it considers the request and an appeal by the Italian prosecutors.
He admitted this story to Italian prosecutors, later retracting it and claiming that the money came from someone else.
Italian prosecutors argue that many works in the Hunt collection were of dubious provenance.
Still, Italian prosecutors continued to gather evidence for a possible criminal case.
Italian prosecutors brought legal proceedings against six people in connection with Senna's death.