Abdel-Malik Nabil Petitjean, the man identified Thursday as the second assailant in this week's attack on a French church the left an octogenarian priest dead, is purported to appear in an Islamic State video calling for more violence.
In the video, distributed by the group's propaganda arm, the Aamaq News Agency, the man purported to be Petitjean calls on his "Muslim brothers to wake up and attack the countries of the allied forces and attack the Westerners with knives and kill them collectively."
He goes on to say that French President Francoise Hollande could now see "we are determined men and we have struck your country and other ... countries of the allied forces as well."
"You will taste what our brothers and sisters have tasted," the man says in a perfect French accent. "We will destroy this country and raise the flag of religion and the word Allah," he added.
The video could not be independently verified.
Petitjean and Adel Kermiche, also 19, have now been identified as the two men who stormed a church during morning Mass on Tuesday, taking hostages before executing Jacques Hamel, 86.
The prosecutor's office said Petitjean was formally identified by DNA comparison. He was named two days after Kermiche, a man who was known to French anti-terrorism authorities, was identified.
During the attack, prosecutors say Petitjean and Kermiche entered the church in the village of Saint-Etienne-du-Rouvray in Upper Normandy and took six hostages, including three nuns, before one escaped to alert the police.
Hamel was killed by knife wounds to the throat and chest, while another person was seriously injured. The two assailants were killed by police. Hours after the attack occurred, the Islamic State extremist militia claimed that it had been carried out by two of its "soldiers."
Islamic State released another video one day after the attack that purportedly showed the two men: one with a scarf around his head, holding a placard with an Islamic State slogan, and the other clad in military fatigues.
In the video both men pledged allegiance to Islamic State leader Abu Bakr al-Baghdadi. That video could also not be independently verified.
French media reported that Petitjean had been flagged by anti-terrorism authorities at the end of June after he tried to depart for Syria. RTL radio also reported that his photo, without a name, was disseminated to police by anti-terrorism authorities - who had received a tip-off to a possible plan by foreign intelligence - three days before the attack.
Petitjean lived in Aix-les-Bains, in the north-east of France and hundreds of kilometres away from the site of the attack, according to RTL and other French media. It was not immediately clear how he met Kermiche, who had also twice tried to depart for Syria and who was under house arrest with an electronic surveillance bracelet.
Facing a wave of attackers with distinct profiles, unusual weapons and low-profile but highly symbolic targets, France is struggling to anticipate threats. With security forces stretched thin after months of extraordinary patrols, President Hollande announced that the country would create a national guard.
Hollande said he had decided to form the national guard based on existing operational reserve forces, with the aim of creating a body "in the service of the protection of the French." The army is already deployed to protect religious sites and other areas of national importance.
He added that the country's defence council would be convened at the beginning of August, followed by consultations with parliamentary commissions in September, with the aim of starting the guard "as fast as possible." France has also recently started a campaign to encourage people to join the military reserves.
France previously had a national guard from 1789 to 1872, which was separate from the army and whose members were active during the country's revolutions.