19 year old Adel Kermiche, who slit the throat of an elderly priest in France Yesterday

Adel Kermiche, was among the ISIS knifemen who stormed a church in Normandy before he slit the throat of an elderly priest. The 19-year-old 'ISIS soldier' was being monitored with an electronic ankle tag after he was arrested for twice attempting to flee France to join the terror group in Syria.

Despite having been released early from prison, Kermiche's bail conditions allowed him to roam unsupervised between 8.30am and 12.30pm, leaving him free to murder the priest in the attack carried out between 9am and 11am.

Kermiche and his accomplice - also known to French police - forced 84-year-old Father Jacques Hamel to kneel before filming themselves butchering him and performing a 'sermon in Arabic' at the altar of the church in Saint-Etienne-du-Rouvray, according to witnesses.

Both were shot dead by police marksmen as they emerged from the building shouting 'Allahu Akbar' following the attack that also left a nun critically injured.

Sister Danielle, a nun who escaped, said: 'They told me "you Christians, you kill us". They forced him to his knees. He wanted to defend himself. And that's when the tragedy happened. They recorded themselves. They did a sort of sermon around the altar, in Arabic. It's a horror.'

French President Francois Hollande, who visited the scene on Tuesday, said the country is now 'at war' with ISIS after the terror group claimed responsibility.

French authorities admitted that both Kermiche and his partner were subject to security 'S' files, meaning they were known terror suspects who should have been under surveillance. 

Kermiche was living with his parents in Saint-Etienne-du-Rouvray with an electronic tag on his ankle, after spending time in prison in both France and Switzerland

Parisian prosecutor Francois Molins revealed that the pair were carrying between them a fake explosives belt with a kitchen timer wrapped in tin foil, a backpack full of fake guns and three knives during the attack, and said they used nuns as human shields. 

Kermiche, pictured in 2011, had previously spent time in prison in France and Switzerland after twice attempting to flee the country to join ISIS in Syria. He was under police surveillance with an electronic ankle tag

19 year old Adel Kermiche, who slit the throat of an elderly priest in France Yesterday