Socrates's lawyer, Joao Araujo, told reporters that after a preliminary hearing yesterday the investigating judge decided he needs to ask Socrates more questions. He said the interrogation will continue today.
The judge must rule whether Socrates should be released or held pending a trial.
Socrates, who was Portugal's center-left Socialist prime minister from 2005 to 2011, was detained by police late Friday.
The Attorney-General's office said he and three others are suspected of colluding in crimes.