|Drusus Minor. Source: Cleveland Museum of Art|
The head of Drusus Minor is clearly recognisable from the archive photographs (Scarpati 2008-11: 357, fig. 7, 358 fig. 10). The head passed through PIASA in Paris in 2004, a source that is not without some interest. It was acquired from Phoenix Ancient Art in 2012. (See Gill 2013: 72 for oral histories and objects linked to this dealer, and with a specific mention to the portrait of Drusus.)
David Franklin, the then director of the Cleveland Museum of Art, defended the acquisition of the head at the time. (He resigned from the museum in 2013.) The museum is probably wishing that it had not claimed that the collecting history had been traced back to the 19th century.
The trail of the Drusus portrait had been identified by a companion piece. The head of Tiberius appears to be the one in a North American private collection ("The Magdalene Tiberius") and published by John Pollini (Pollini 2005; Scarpati 2008-11: 361 figs. 11-14). It was reported to have formed an old French collection in Marseilles dating to the 1960s. It was said to have been found in North Africa (a good reminded of the intellectual consequences of collecting recently surfaced archaeological material). It was acquired by its present proprietors in 2004. The source appears to have been the Royal-Athena Galleries (Art of the Ancient World 15  no. 24; Scarpati 2014: 33 fig. 9). Will those owners be contacting the Italian authorities in the light of the return of the Drusus portrait?
It is interesting that the (recent) collecting histories of both portraits now do not seem to go back beyond 2004 (i.e. 34 years after the UNESCO Convention). What were their collecting histories immediately prior to 2004?
The Drusus Minor return is merely serving to open up the discussion. Was the Cleveland Museum of Art aware of Scarpati's research prior to the portrait's acquisition?
Now is probably also a good time for the museum staff to revisit the documented collecting history of the Leutwitz Apollo.
Gill, D. W. J. 2013. "Context matters: The Cleveland Apollo goes public." Journal of Art Crime 10: 69-75. [academia.edu]
Pollini, J. 2005. "A new marble head of Tiberius. Portrait typology and ideology." Antike Kunst 48: 55-72. [JSTOR]
Scarpati, G. 2008-11. "Un ritratto di Tiberio da Sessa Aurunca ritrovato note su un probabile ciclo Suessano di statue onorarie Giulio-Claudie." Rendiconti della Accademia di Archeologia Lettere e Belle Arti 75: 345-68. [Academia.edu]
Scarpati, G. 2014. "Il ritratto di Druso minore dal ciclo statuario Giulio-Claudio di Sessa Aurunca." Bollettino d’Arte 24: 29-38. [Academia.edu]
"Cleveland Museum of Art to Transfer Roman Sculpture of Drusus Minor to the Republic of Italy", Cleveland Museum of Art April 18, 2017. [press release]
"Il Cleveland Museum of Art restituisce all’Italia una scultura romana di Druso Minore", MiBACT April 18, 2017. [press release]