One of the two attackers who held five people hostage in the church has been identified as 19-year-old Adel Kermiche.
France's anti-terrorism unit said that Kermiche had been arrested in March 2015 in Germany, Bild reported, after trying to reach Syria via Turkey from Munich airport. He had reportedly tried to travel using his brother's passport.
After this failed attempt, the teenager later managed to reach Turkey from Geneva airport using a different family member's passport, according to Swiss newspaper Tribune de Genève. He was apprehended in Turkey in May, before being sent back to Switzerland and then to France.
Kermiche spent about ten months in prison charged with "plotting to prepare a terrorist attack", however he had been released on May 2nd this year under judicial supervision.
Since his release, Kermiche had been living with his parents and wearing an electronic tag. He was only allowed to leave the house between 8:30 and 12:30 each day, however the attack on the church in the northern town of Saint-Etienne-du-Rouvray took place within that time, at 9:45 during morning mass.
The attack has been claimed by Isis. The two men slit the throat of an 86-year-old priest and left another person seriously injured.
Now, questions are being asked in France as to how a man known for terrorism-related offences and under surveillance was able to carry out such an attack.
In the local area, Kermiche's extremist views were well-known.
One man who knew him told Le Parisien newspaper he was like a "ticking time-bomb" and that all he talked about "was his desire to go to Syria and kill Bashar al-Assad's soldiers".
Kermiche's companion has not yet been identified, according to Paris prosecutor François Molins, who spoke on Tuesday evening. Both men were shot and killed by police.