The list contained names of police, politicians, journalists and public figures
French police say the knifeman who killed a senior policeman and his partner had a hit list of high-profile targets.
Prosecutor Francois Molins told a news conference that killer Larossi Abballa had a list containing the names of police, politicians, journalists, rappers and other public figures.
The list was found after the siege in Magnanville, about 35 miles (55km) west of Paris. No further details were given.
Police also found three telephones, three knives "and in particular a bloodied knife lying on the table", in the house.
Mr Molins said Abballa had declared allegiance to Islamic State leader Abu Bakr al-Baghdadi, and had threatened to kill non-believers and their families wherever they live.
Abballa made the statements in exchanges with police during a three-hour stand-off on Monday.
He repeatedly stabbed 42-year-old Jean-Baptiste Salvaing and killed his partner, who also worked for the police.
The couple's three-year-old son was also held hostage - he was found unharmed but in shock.
Abballa posted a 12-minute video of the attack, which was distributed to more than 100 friends and contacts. In it, he considered what to do with the three-year-old.
Police have also revealed that Abballa knew the policeman he attacked.
The news agency Amaq, which is linked to Islamic State, quoted an unnamed source as saying an IS fighter carried out the attack.
French authorities said they have "no reason" to doubt the claim.
Mr Molins said three people - aged 27, 29 and 44 - have been detained in the investigation. He did not provide any other details.
Abballa had been under wiretap surveillance since January as part of an investigation into a Syrian jihadi network.
But that operation had given no clue to the upcoming attack, said Mr Molins.
Abballa was sentenced in September 2013 to two-and-a-half years in prison over his role in a jihadist group with links to Pakistan, but was freed because of time already served awaiting trial.
French President Francois Hollande said earlier it was "incontestably a terrorist act" and that France faces a threat "of a very large scale".