Francisco Granados standing behind former Madrid premier Esperanza Aguirre. Álvaro García

The Civil Guard launched a major raid on Monday morning against politicians, municipal workers and construction firms suspected of involvement in a bid-rigging scheme.

Francisco Granados, a former member of the Madrid regional government, has been arrested as part of the ongoing Operation Púnica.

Another 50 individuals have also been detained in an operation that took place simultaneously in Madrid, Murcia, León and Valencia. Authorities said more arrests could take place as the day progresses.

Detainees include the head of the provincial authority of León, Marcos Martínez Barazón, of the Popular Party (PP). He was appointed five months ago to replace Isabel Carrasco, who was shot dead in the street in broad daylight by a disgruntled ex-employee.

The mayors of Valdemoro, José Carlos Boza Lechuga (of the PP) and Parla, José María Fraile (of the Socialist Party), are also under arrest.

Local councilors and civil servants are also suspected of participating in a scheme that awarded €250 million worth of public contracts in the last two years.

Several constructors have been arrested as well. Preliminary evidence shows the existence of a ring of corrupt entrepreneurs who paid politicians to secure beneficial decisions for their companies.

Francisco Granados, the highest-placed former official involved in the case, had a Swiss bank account between 1999 and late 2012, when he withdrew all of his money at once. Swiss authorities then informed Spain that Granados had held €1.5 million in this account.

A former head of the PP’s Madrid branch between 2004 and 2011, Granados was also top aide to Esperanza Aguirre, a former Madrid premier and a very influential figure within the center-right party. He was also mayor of Valdemoro, a town of 72,000 residents south of Madrid, between 1999 and 2003.

High Court judge Eloy Velasco has been investigating the origin of his fortune for a year, and suspects that it may come from illegal commissions paid by builders for fraudulent rezoning of land and rigged construction bids while Granados was mayor of Valdemoro.

On February 19, newspaper El Mundo revealed that Granados made his first deposit into the Swiss-based BNP Paribas just a few months after becoming mayor of Valdemoro and quitting his stockbroker job. Granados initially denied the existence of this account, then admitted to it but said he never made deposits while an elected official.

But the scandal got him removed from office by Aguirre in November 2011.

Granados is also involved in the wider Gürtel bribes-for-contracts case and in a political espionage case.