The market value of the five artworks was estimated to be above 25 million euros (USD 27.8 million).
Police arrested seven suspects linked to the theft last year and three more in January this year. No details were available immediately, a police spokeswoman said today.
The paintings were part of a collection owned by a close friend of Bacon in central Madrid, according to earlier reports.
The figurative Irish-born artist spent time studying old master paintings in the Spanish capital's Prado Museum. He died in the city in 1992 at age 82.