A judge has charged former Portuguese Prime Minister Jose Socrates with corruption and ordered him held in custody pending a final decision on whether he stands trial.
Judge Carlos Alexandre said Monday there was sufficient evidence of tax fraud and money-laundering to hold Socrates on suspicion of wrongdoing.
Prosecutors will now conduct further investigations before presenting formal charges.
A magistrate will then decide whether to put Socrates on trial.
Police arrested the 57-year-old at Lisbon airport Friday as he arrived back from Paris.
Socrates has been living in France since his resignation in 2011.
Officials refused to provide details and it was unclear if the inquiry, known as "Operation Marquis," was linked to Socrates' time as prime minister from 2005 to 2011.
As prime minister, Socrates was investigated several times, including on allegations he misused his post as environment minister in 2002 to allow the construction of a shopping mall.
He denied wrongdoing and faced no formal charges.