"This is a suit against unnamed persons for murder with aggravating circumstances concerning those who gave the orders at the top of the police" during the assault on Merah's flat in Toulouse, said lawyer Isabelle Coutant-Peyre.
Mohamed Benalel Merah said in March that he wanted to sue the RAID elite police unit that shot dead his son on March 22 during a shootout at the end of a 32-hour siege at his flat in the southern French city.
The 23-year-old had shot dead three soldiers, and three children and a teacher at a Jewish school, in a wave of killings that shocked the country.
He filmed himself carrying out the attacks and reportedly confessed to police before he was shot dead.
"You've got 300 to 400 heavily armed people and a guy shut up all alone in his apartment. That alone is enough to raise questions," said Coutant-Peyre, who is part of Merah's legal team headed by Algerian lawyer Zahia Mokhtari.
She said the family had video evidence that would be handed over to the authorities when they requested it.
Mokhtari said in April that she had proof that Merah was "liquidated", including two 20-minute videos probably filmed by Merah himself before he was shot dead.