French authorities have filed the first charges tied to the killing of a priest in a church in Normandy, as the government announced on Friday it would consider a temporary ban on foreign financing of mosques.
A 19-year-old man was charged with "criminal conspiracy with terrorists" and locked up over the video on a mobile phone police discovered at his home, a judicial source said.
Three other people were still being held by authorities for questioning.
Three days before the Tuesday attack authorities found a video showing one of the assailants, Abdel Malik Petitjean, pledging allegiance to the Islamic State group and speaking of "a violent action".
The charges came as French Prime Minister Manuel Valls said he would weigh a temporary ban on foreign financing of mosques, urging a "new model" for relations with Islam after a spate of terror attacks.
Valls, under fire for perceived security lapses around the attacks, also admitted a "failure" in the fact that one of the assailants who stormed the church, 19-year-old Adel Kermiche, had been released from prison while awaiting trial on terror charges after his second attempt to travel to Syria. Kermiche's accomplice Petitjean, also 19, had been on the security watch list since June after trying to reach Syria from Turkey.
In an interview with Le Monde newspaper, he said he was "open to the idea that, for a period yet to be determined, there should be no financing from abroad for the construction of mosques".
The socialist prime minister also called for imams to be "trained in France, not elsewhere". He said interior minister Bernard Cazeneuve, whose portfolio also includes religious affairs, was working on building a "new model" for France's relations with Islam. And Salafism, an ultra-conservative brand of Sunni Islam "has no place in France", Valls said.
France has just over 2,000 mosques, for Europe's largest Muslim populations which numbers around five million. Some large mosques have been financed by Saudi Arabia and other Gulf or northern African countries, according to local media reports.
After meeting with President Francois Hollande earlier this week, the rector of the Paris Mosque Dalil Boubakeur himself suggested "certain reforms of the institutions" of Islam.
In northern Saint-Etienne-du-Rouvray where 85-year-old priest Jacques Hamel was killed, Muslims and Christians gathered together in mourning after the attack that hit their town. "You share our pain. This pain is also yours," Reverend Auguste Moanda said, in a rare speech given during Friday prayers at the local mosque.
Both Valls and Cazeneuve have faced calls to resign after the second jihadist attack in less than a fortnight raised questions over France's vigilance and preparedness.
The government has faced tough questions since it emerged that both church attackers had been on the radar of intelligence services and had tried to go to Syria.
On Friday, L'Express magazine revealed that Kermiche had described the modus operandi of the attack on the encrypted messaging app Telegram. "You take a knife, you go into a church. Bam!" says a chilling message recorded just a few days before the attack.
A source close to the investigation confirmed the authenticity of the message, according to L'Express. Other messages speak of the influence of a "sheikh" Kermiche met in prison, his wish to set up a terrorist cell and details of his failed attempts to reach Syria.
Some 200 people were in the Telegram group receiving the messages, L'Express said. The church attack came as the government was already facing a firestorm of criticism over alleged security failings after the Bastille Day truck massacre in Nice that left 84 people dead two weeks ago.
In the government's first admission of a lapse since the two attacks, Valls acknowledged Kermiche's liberty was a "failure, it has to be recognised", adding that judges needed to take a "different, case-by-case, approach, given the jihadists' very advanced concealment methods". But he said it was "too easy to hold judges responsible for this act of terrorism."