One of the men suspected of killing a priest at a church in northern France was being monitored by police and was wearing a surveillance tag at the time of the attack, officials say.
Prosecutor Francois Molins said Adel Kermiche, 19, was twice arrested last year trying to reach Syria.
Kermiche and a fellow attacker stormed the church in Saint-Etienne-du-Rouvray, a suburb of Rouen, during morning Mass.
They slit the throat of the elderly priest before being killed by police.
One of four people taken hostage – said to be an elderly parishioner – suffered severe knife wounds, Mr Molins said.
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Mr Molins said the two attackers had been carrying a “fake explosive device covered in aluminium foil” along with hand-held weapons when they entered the Catholic church.
As they targeted Father Jacques Hamel, in his 80s, some of the congregation were able to escape and alert the police, who sent in a team specialised in dealing with hostage situations.
Three of the hostages were used as human shields to block the police from entering the church, Mr Molins said.
When they were eventually let go, the two attackers followed them out of the church shouting “Allahu Akbar” before being killed, Mr Molins said.
Earlier, the so-called Islamic State (IS) claimed its “soldiers” carried out the attack.
A nun, who identified herself as Sister Danielle, had been in the church at the time and described what happened.
“They forced [Fr Hamel] to his knees. He wanted to defend himself, and that’s when the tragedy happened,” she told French media.
“They recorded themselves. They did a sort of sermon around the altar, in Arabic. It’s a horror”.
Residents of the town have reacted with shock and sadness to Fr Hamel’s killing. They spoke of a well-loved priest who had been dedicated to his parish.
Local Imam Mohammed Karabila said he was “stunned by the death of my friend. He was someone who gave his life to others”.
What we know of Adel Kermiche?
- First tried to leave for Syria in March 2015. His family reported him missing and he was arrested in Germany, using his brother’s identity card
- Returned to France, charged and placed under judicial supervision
- Tried again to head to Syria in May 2015, reaching Turkey before being arrested again and returned to France
- Remained in custody until March 2016 when he was released on condition he wear an electronic surveillance tag and remain at his home in Saint-Etienne-du-Rouvray except for weekday hours between 08:00 and 12:30
Mr Molins said investigators were still working to identify the second attacker.
He said an Algerian-born 17 year old had been taken into custody – the younger brother of a suspect “wanted under an international arrest warrant for having left for the Iraq-Syria zone”.
‘We will not be afraid’: Adam Fleming reports from the scene
This quiet suburb, a few miles from the cathedral city of Rouen, is quieter than usual after this morning’s horrific events. The heavily armed police have set up a large cordon around the church; a row of white tents – presumably for forensics officers – obscures the view. The nearby supermarket is closed and its car park is being used by journalists rather than shoppers.
Locals seem shocked, but not in a dramatic way. A man told me how he had conducted christenings, marriages and funerals for years alongside Father Hamel. He showed me a set of keys – keys for the church. “When I heard the news of his death, it was like being hit on the head from above. I just want to go to the church but I can’t,” he said.
A priest from a neighbouring parish, who also knew Fr Hamel, passed through on his way to conduct his own mass. His message tonight will be that this is not an attack on the Catholic Church – it is merely the latest symbol of French life to be targeted.
And the mood of some here was summed up by a woman cycling past the waiting media, who shouted to no-one in particular: “We will not be afraid.”
French President Francois Hollande appealed for “unity” as he warned that the war against terrorism “will be long”.
“Our democracy is the target, and it will be our shield. Let us stand together. We will win this war,” he said.
France is still reeling from the Bastille Day attack in Nice earlier this month, when a lorry was driven into celebrating crowds by Tunisian Mohamed Lahouaiej-Bouhlel, killing more than 80 people.