Hussein Salem, 77, his son and an associate described as a front man were arrested in a wealthy Madrid suburb. The money was allegedly obtained illegally in Egypt and sent to accounts in Spain held by Salem, his family and his business empire. Police also seized homes worth 10 million euros ($14 million).

Salem appeared Friday before two judges: one handling the Spanish money laundering probe and another dealing with the international warrant under which Salem was arrested at the request of Egypt.

Salem also holds a Spanish passport, a court official said on condition of anonymity in line with court policy.

One of the most secretive businessmen in Egypt, Salem is wanted in his country on charges of bribing Mubarak and his family and squandering public funds, Egyptian officials say.

His detention was seen in Egypt as a major step toward unraveling secrets of corruption throughout the reign of Mubarak; and possibly a key to locate and retrieve much of Mubarak's riches, believed to be stashed abroad at a time when the country's economy is depressed, months after the uprising. Some estimate Mubarak's holdings at tens of billions of dollars.

Salem left Egypt a week before Mubarak was forced to resign on Feb. 11. Salem was charged last month along with Mubarak and the ex-president's two sons. Their trial is scheduled for Aug. 3.