Septimius Severus from Santa Maria Capua Vetere

It has been reported (by ARCA) that a portrait of the emperor Septimius Severus that had been stolen from the Antiquarium of Santa Maria Capua Vetere in November 1985 has been seized at Christie's New York (June 2020) after being offered at auction by them on 28 October 2019, Faces of the Past: Ancient Sculpture from the Collection of Dr. Anton Pestalozzi.

According to the stated history, the head first passed to Jean-Luc Chalmin, London. Chalmin also supplied antiquities to the Stanford Place collection and to the Fleischman collection (apparently the fourth most important supplier). The Severus then passed to Galerie Arete in Zurich in 1993. (The same gallery appears to have handled ex-Becchina material.) It was then sold to Dr Pestalozzi.

How did the portrait appear at auction when it had been reported as stolen? Was the history of the piece checked? What was the due diligence process?

Drusus from an old Algerian collection

Source: Cleveland Museum of Art

The Cleveland Museum of Art purchased a marble portrait head of Iulius Caesar Drusus Minor (Steven Litt, "Cleveland Museum of Art buys important ancient Roman and Mayan antiquities", Cleveland.com August 12, 2012). The head head has been purchased from Phoenix Ancient Art for an undisclosed sum. Litt provides the collecting history:

The museum said the portrait of Drusus Minor was the property of the Bacri family of Algiers, Algeria, as far back as the late 19th century. The museum said the work was inherited by Fernand Sintes before 1960s, and that Sintes transferred it to France in 1960.

The museum has yet to disclose the authenticated documentation for this reported "pedigree". David Franklin, the director of the Cleveland Museum of Art and expert in Italian Renaissance art, informs the report:

Franklin said the two new purchases follow guidelines established by the Association of Art Museum Directors, which stipulate that museums generally should avoid buying antiquities unless they were documented as being outside their likely country of origin before 1970, the date of an international UNESCO convention aimed at halting the looting of antiquities, or were legally exported thereafter.

What is the evidence that Drusus was known prior to 1970? Franklin appears to expect that questions will be asked about the Drusus.

Cleveland is unwilling to discussion its acquisition of the bronze portrait of Marcus Aurelius that appears to come from Bubon. The collecting history for the so-called Cleveland Apollo (also acquired from Phoenix Ancient Art) has been disputed.

Cleveland was one of the North American museums that agreed to return material to Italy (list here). So there is every reason for the museum to wish to be seen to be conducting a rigorous due diligence process prior to acquisition.

The dispute over the St Louis Art Museum's acquisition of an Egyptian mummy mask, purchased from Phoenix Ancient Art, has shown flaws in the reported collecting history.

The second piece acquired by Cleveland is a Mayan vessel "with a Battle Scene" had apparently passed through the hands of Edward H. Merrin in 1973. (Edward H. Merrin had also handled the "Merrin Zeus" displayed at the Cleveland Museum of Art.)