Spanish police have made seven arrests in relation to the theft of five Francis Bacon paintings from a private home in Madrid last year with an estimate combined worth of €25 million (approximately $28 million).

According to a statement from Spanish police, in February, investigators received an email from a British private company which specializes in tracking stolen artworks. The company claimed that a person had gotten in touch with them via email to establish whether one of the five stolen Bacons was in fact on any list of stolen artworks.

The anonymous sender had also attached photographs of the painting. One of the images showed Bacon’s signature on the back of the canvas, which led the company’s specialists to suspect that the photo was taken after the theft.

The unnamed British company forwarded the photographs to Spanish investigators, who were able to determine the model of the camera that was used, locate the company that rented it out, and subsequently, find out who had rented it. The renter turned out to be one of the perpetrators. He was detained in his home, alongside a second perpetrator.

Photo of a pair of the stolen Francis Bacon Paintings. Photo: Courtesy Spanish Police.

As for the five remaining abettors, the investigators found out that the thieves had been in touch with a Madrid-based art dealer and his son, who turned out to be the ones who had gotten in touch the British company to inquire about the status of one of the stolen works.

Three further individuals, who were contacted by the dealers and offered the stolen works, were also identified and arrested.

However, the paintings themselves have not been located yet, and the investigation is ongoing.

Spanish police also revealed that besides the paintings, the thieves stole a safe containing several collections of coins, jewels, and other valuable goods.

The theft—arguably one of the biggest art heists to take place in Spain in the last few decades—occurred in July 2015, when the five artworks and other valuable goods were stolen from the Madrid apartment of José Capelo Blanco, a Spanish friend of the legendary painter who inherited the artworks when Bacon died in 1992.

Capelo Blanco was in London when the theft occurred, according to Spanish police. An international investigation was launched shortly thereafter, but the heist was only made public in March this year.

At the time, ABC reported that Capelo Blanco was Bacon’s last lover during a relationship that lasted four years, until Bacon’s death in Madrid in 1992.

The Spanish newspaper reported that the legendary painter met the young financier at a party in the honor of the choreographer Frederick Ashton, when Bacon was 78 years old and Capelo 35. Capelo went on to pose for the artist on several occasions, including for a 1987 portrait and a 1991 triptych that is currently part of the MoMA collection.