Three Old Master paintings were stolen from a small art museum in an Oxford college over the weekend. The 16th- and 17th-century works by Anthony Van Dyck, Salvatore Rosa, and Annibale Carracci are thought to be worth as much as $12 million.

The burglary at the Christ Church Picture Gallery at the University of Oxford occurred at around 11 p.m. on Saturday, March 16. It is unclear how the burglars accessed the gallery.

The stolen paintings are Rosa’s A Rocky Coast, With Soldiers Studying a Plan (late 1640s), Van Dyck’s A Soldier on Horseback (around 1616), and Carracci’s A Boy Drinking (around 1580). Similar works by the three arists could fetch as much as £10 million ($12.3 million) on the art market, according to the Times.

Police are appealing for witnesses who saw or heard anything suspicious to come forward, as well as anyone who might have CCTV or other footage from the area around the time of the crime.

“The artwork has not yet been recovered but a thorough investigation is underway to find it and bring those responsible to justice,” a statement from Thames Valley Police says. It adds that there will be an increased police presence in the area while officers and staff carry out enquiries.

The works have been at Christ Church college since 1765, when General John Guise (1682-83–1765) left more than 200 paintings and nearly 2,000 drawings to his alma mater. The college’s Old Master collection is renowned internationally, and includes works by Leonardo and Raphael, among others. They are housed in the purpose-built Christchurch Picture Gallery, which opened 1968.

The gallery is staying closed until further notice.

Targeted raids on smaller institutions with valuable collections seems to be a growing occurrence after a thief attempted to heist a pair of Rembrandts from Dulwich Picture Gallery in November. In Oxfordshire a very different audacious heist took place at Blenheim Palace last October when Maurizio Cattelan’s solid-gold toilet, America, was stolen. The sculpture is still missing although three people have been arrested in connection with the theft.