State prosecutor Frédéric Fèvre told the AFP news agency that a thorough investigation of Faïd’s prison break had begun.
Faïd's brother was taken in for questioning on Sunday, as he often visited the prisoner.
“Obviously, he had one or more accomplices,” said Fèvre. “The investigators will now determine how he was able to obtain explosives and a weapon.”
French officials have warned that Faïd is thought to be armed and dangerous.
Besides issuing a Europe-wide arrest warrant for Faïd, France has called upon Interpol for help, amid suspicions he may have fled to nearby Belgium.
Police have said prison workers were not at fault for Faïd’s breakout, as it had seemingly been planned meticulously.
Faïd escaped from the Sequedin prison on Saturday by blasting through five prison doors using explosives, before taking four prison guards hostage.
Faïd released all the hostages shortly after his escape, before setting fire to his getaway car and leaving in a second vehicle.
Nicknamed “The Writer,” Faïd published a book in 2010 about how he was ready to turn his back on his life of crime.
However, Faïd was suspected of masterminding an armed robbery in 2010 in which a policewoman was killed, and had been serving the remainder of his original sentence at Sequedin prison since 2011 for failing to comply with his parole conditions.