The two masked men apparently left behind a getaway car, which police impounded. CNN affiliate BFMTV reported that police found an identification card of one of the Kouachi brothers during their investigations.
"It was their only mistake," said Dominique Rizet, BFMTV's police and justice consultant, reporting that the discovery helped the investigation.
The Kouachi brothers returned from war-torn Syria in the summer, USA Today reported without saying where it got the information.
Officials were running their names through databases to look for connections with ISIS and al Qaeda. The suspects were known to security services, Valls said.
A third suspect, 18-year-old Hamyd Mourad, has turned himself in to police, a source close to the case told the AFP news agency. Mourad did so late Wednesday after seeing his name mentioned on social media, the source said.