Italian police have arrested 12 suspects in connection to the stunning November heist of 17 Old Master paintings worth €15 million ($16 million) from Verona’s Castelvecchio Museum, reports the Association for Research into Crimes Against Art (ARCA).

The suspects, are Moldovan and Italian, were identified thanks to a joint investigation by Verona police and the arm of the Italian military police devoted to the protection of cultural heritage, according to the Corriere del Veneto.

The crime, which took place just before the museum closed on November 19, 2015, now appears to have been an inside job. Allegedly, the museum’s security guard’s brother was dating the sister of one of the perpetrators.

During the robbery, one thief held the museum cashier at gunpoint while the guard reportedly was forced to guide the other burglars through the building for a leisurely hour-long heist. Then, they stole his keys, using his car as a get-away vehicle.

Hans de Jode, Porto di mare.
Photo: courtesy Museo di Castelvecchio, Comune di Verona.

Following their investigation, police now believe the guard, who worked for Securitalia, a company contracted by the museum, actually assisted in the crime and left his keys in his car ahead of time for the robbers’ use.

The guard was among those arrested, but the missing paintings, which include works by Peter Paul Rubens, Andrea Mantegna, Giovanni Francesco Caroto, Hans de Jode, Jacopo Bellini, and Jacopo and Domenico Tintoretto, have not yet been recovered.

Following the robbery, Italian politicians were outspoken in their outrage, and wild rumors flew, with some speculating that the paintings would be sold to fund ISIS. The radical terrorist group is believed to bankroll its activities in part by the the smuggling of looted ancient antiquities.

“We hope to recover all the paintings and that they are in good condition,” said Verona mayor Flavio Tosi in a statement.

See more images of the stolen paintings below.

Andrea Mantegna, sacra famiglia con una santa.
Photo: courtesy Museo di Castelvecchio, Comune di Verona.

Peter Paul Rubens, dama delle licnidi.
Photo: courtesy Museo di Castelvecchio, Comune di Verona.

Jacopo Bellini, San Girolamo penitente.
Photo: courtesy Museo di Castelvecchio, Comune di Verona.

Jacopo Tintoretto, Madonna allattante.
Photo: courtesy Museo di Castelvecchio, Comune di Verona.