The Serious Fraud Office has made three arrests and searched multiple properties in England and Monaco as part of an investigation into bribes paid by a construction firm to win a contract to help build a data center for Microsoft Corp.

Former associates of the Mace Group, a London-based construction group, and infrastructure firm Blu-3 are the subjects of the SFO’s investigation, according to an announcement on Wednesday. Individuals at Blu-3 are accused of paying over £3 million ($4 million) in bribes to Mace associates to win contracts to help build the data center in the Netherlands.

More than 70 SFO staff searched four homes and one commercial property across London, Kent, Surrey and Somerset to seize evidence, the SFO said.