His rap sheet meanwhile paints a picture of a seasoned criminal, well-used to courts and spells behind bars.
Born in Paris, he had a string of criminal convictions for armed robbery, drug dealing, violence and receiving stolen goods. He was jailed for five years in 2001 for armed robbery, and again in 2009 for drug dealing.
Paris prosecutor Francois Molins said Ben Belgacem had shown signs in 2011 and 2012 of having radicalized in jail. His home was searched in 2015 on suspicion of links to radical Islam, but no incriminating evidence was found.
The man's father, brother and cousin were detained for questioning on Saturday, according to Molins, all of them having approached police themselves. Police also searched Ben Belgacem's home in the northeastern Paris suburb of Garges-les-Gonesse, in the multi-ethnic Seine-Saint-Denis area. Officers found a machete and several grams of cocaine in the apartment.
Positioning her as a shield, he pointed his revolver to her temple, Molins told a press conference.
“Put your weapons down, hands on your heads. I'm here to die for Allah. In any case people are going to die,” he told the soldiers.
He scuffled with the female soldier, trying to take her assault rifle and succeeding after a couple of attempts.
She then dropped to her knees, giving her colleagues the opportunity to shoot at him. He tried again to use her as a shield, but a third shot killed him at 8:25 am, Molins said.
A subsequent search found he had brought along a petrol can in a backpack. He also had in his possession a 9mm revolver, 750 euros ($805), a copy of the Koran as well as a packet of cigarettes and a lighter. No-one else was injured in the melee.
Identity documents found on the attacker matched those presented by the man who fired at police in Garges-les-Gonesse.
Neighbours described him to AFP as a withdrawn, serious man who nobody really knew. He seemed lonely, they said.
No one had any idea of his spells in prison, although since his most recent release from jail in September, he had been under judicial monitoring.
“The last time I saw him was three days ago. He had a determined air, as if he wanted to fight with his family or colleagues,” said one neighbour Hamid.
“Sometimes, we'd meet in the elevator, that's all. He always wore sports clothes. He has a scary face, a real devil,” said Hatice, another neighbour.
At this stage, there is no indication Ben Belgacem had made trips overseas, according to the Paris prosecutor, unlike many other radicalized Islamists.
He was a regular at an Italian-Cuban bar in the south of Paris, which was known for its rowdy nights, a local said.
It was to this venue he headed immediately after drawing a gun and firing at officers earlier Saturday, slightly injuring one in the head. He then burst into the bar, threatened customers and fired again without injuring anyone.
Telling his relatives by phone that he had been up to some “mischief”, he then drove towards what prosecutors described as the “crescendo” of his destructiveness, stealing a car and heading towards the airport.