A Frenchman suspected of killing two police officers declared his allegiance to Islamic State (IS) leader Abu Bakr al-Baghdadi and threatened to kill non-believers, according to Paris prosecutor Francois Molins.
Attacker Larossi Abballa made the declaration in exchanges with police during a stand-off on Monday night at a house in the Paris suburb of Magnanville, where a police commander and his partner were found dead.
Mr Molins said Abballa, who was also found dead in the house after the stand-off, responded to IS calls to kill non-believers and their families wherever they live.
The couple's three-year-old child was found unharmed in the property after the stand-off.
Abballa is said to have filmed the knife attack before posting it on Facebook Live.
A police official said that at one point in the video, the attacker puzzles over what to do with the child.
IS news agency Amaq cited an unnamed source as saying an IS fighter carried out the attack.
Prosecutor's office spokeswoman Agnes Thibault-Lecuivre said French authorities have "no reason" to doubt that claim.
Abballa had a list of targets, including journalists and public figures, according to Mr Molins.
Searches of Abballa's home had tuned up a list of "rappers, journalists, police officers and public personalities".
Mr Molins give no further detail on the list, or whether it had specific names.
Mr Molins said Abballa stabbed Jean-Baptiste Salvaing, 42, a police commander in the Paris suburb of Les Mureaux, outside his home on Monday night.
He then went inside and took Salvaing's partner and three-year-old son hostage. He killed the woman, who was a police administrator in the suburb of Mantes-la-Jolie, but did not harm the boy, Mr Molins said.
Abballa recorded a 12-minute video related to the attack and posted it on Facebook, Molins said, but he did not provide further details.
The prosecutor added Mr Molins said three people - aged 27, 29 and 44 - were detained as part of the investigation.