Twelve Old Master paintings worth an estimated €4 million ($5.5 million) have been returned to the Museo Nazionale San Matteo di Pisa (National Museum of San Matteo, Pisa), according to the AGI. The works were missing from the museum for more than 10 years. Yet, for most of the time, no one even knew to look for them.

Last year Dario Matteoni, the museum’s new director, spearheaded an investigation of the museum’s inventory . The museum then discovered that 12 paintings, which had been sent to a restorer in the city of Lucca in 2002 never returned. That restorer is reported to have been paid approximately €31,000 for his work on a total of 17 canvases for the museum.

Matteoni filed a lawsuit last December, demanding the paintings’ return. That suit led the cultural heritage department of Italy’s national police force to begin an investigation in January 2014. They have since recovered 12 of the works. The restorer had sold six of the paintings to foreign dealers from whom they were confiscated.

The restorer himself turned over the remaining four canvases. Due to Italy’s 10-year statute of limitations on stolen property, the man cannot be criminally prosecuted for keeping the paintings.

The two works that have not yet been recovered have been located by members of the cultural heritage force. They are currently attempting to repatriate the works from a French collection. According to reports, all of the buyers of works from the museum were unaware of their provenance.

“It’s a very unusual situation,” regional director of cultural heritage Isabella Lapi, told La Repubblica, “the first time something like this has happened in my career.” She went on to explain that it is very rare for any restoration work to be contracted to workers outside of the museum system.