All three were interrogated by the police.
French authorities now believe the killer was motivated by Islamic extremism or racism, Israel Radio reported.
It is the third shooting attack in the Toulouse region in just over a week, and the suspect may be linked to all of them. The previous shootings targeted and killed soldiers of North African origin.
The soldiers, part of an elite paratrooper regiment, were let go from the military after a photo of them surfaced of them saluting a Nazi flag with a swastika.
Rabbi Jonathan Sandler, 29, his 4-year-old and 5-year-old sons Gabriel and Arieh, and 7-year-old Miriam Monsonego were killed Monday outside the Ozar Hatorah school in the southern French city.
In the attack, a gunman drove a scooter and used a handgun to shoot and kill the victims. Police believe the killer may have taped the killing, and think he may plan to post the video on the Internet.