The second teenager involved in the killing of a priest in a church in France this week was a 19-year-old who was known to security services as a potential Islamist militant, police and judicial sources said on Thursday.
The man also appears to be a suspect that police were looking for in recent days after a tipoff from a foreign intelligence service that he was planning an attack, the police sources said.
The revelations are likely to fuel criticism by opposition politicians that President Francois Hollande's Socialist government did not do enough to stop the pair given that they were already under police surveillance.
They interrupted a church service, forced a 85-year-old Roman Catholic priest to his knees at the altar and slit his throat. They were both shot and killed by police.
Police have identified the second man as Abdel-Malik Nabil Petitjean from a town in eastern France on the border with Germany, a judicial source told Reuters.
Security services had on June 29 opened a special file on Petitjean for becoming radicalized, a police source said separately. The government has said there are about 10,500 people with so-called 'S files' related to potential jihadi activities in France.
His accomplice, Adel Kermiche, had already been identified by police. He was known to intelligence services after failed bids to reach Syria to wage jihad.
Kermiche, also 19, wore an electronic bracelet and was awaiting trial for alleged membership of a terrorist organization having been released on bail.
Acting on a tipoff from a foreign intelligence agency France's intelligence services sent a photo to various security forces, but did not have a name, sources close to the investigation said.
Police did not have the name of the person in the photo but now have little doubt that it is Petitjean, the police sources said.
The person in the photo appears to be one of two people who can be seen in a video posted on Wednesday by Islamic State's news agency, they said. The video claimed the two men were the church attackers pledging allegiance to the group's leader.
Petitjean's mother Yamina told BFM TV that her son had never spoken about Islamic State. Three people close to Petitjean have been detained in police custody, a judicial source said. A 16-year-old, being held since Tuesday in connection with the attack, is still in custody.
Tuesday's attack came less than two weeks after another suspected Islamist drove a truck into a Bastille Day crowd, killing 84 people.
Opposition politicians have responded to the attacks with strong criticism of the government's security record, unlike last year, when they made a show of unity after gunmen and bombers killed 130 people at Paris entertainment venues in November and attacked a satirical newspaper in January.
Hollande's predecessor and potential opponent in a presidential election next year, Nicolas Sarkozy, has said the government must take stronger steps to track known Islamist sympathizers.
He has called for the detention or electronic tagging of all suspected Islamist militants, even if they have committed no offense.
Kermiche's tag did not send an alarm because the attack took place during the four hour period when he was allowed out.
According to the justice ministry, there are just 13 terrorism suspects and people convicted of terrorist links wearing tags such as the one worn by Kermiche. Seven are on pre-trial bail. The other six have been convicted but wear the electronic bracelet instead of serving a full jail term.
Interior Minister Bernard Cazeneuve rejected Sarkozy's proposal, saying that to jail them would be unconstitutional and counterproductive.
He has said summer festivals that do not meet tight security standards would be canceled, and announced a shift in the deployment of 10,000 soldiers already on the streets, saying more would now be sent to the provinces.
Since the Bastille Day killings in Nice, there has been a spate of attacks in Germany too, creating greater alarm in Western Europe already reeling from last year's attacks in France and attacks this year in Brussels.