Surveillance video of the attack shows the man lunging at officers in the plaza outside the cathedral before being shot.
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France is under a State of Emergency until July following a series of lethal attacks carried out by ISIS and al-Qaeda operatives.
Despite this, a spokesman for the French government, Christophe Castaner, in a radio interview said the man had given no sign of his radicalisation and the attack was believed to be "an isolated act". The attacker remained hospitalized with gunshot wounds.
The unnamed suspect, a 40-year-old man from Algeria, made the declaration of allegiance in a video authorities found in his apartment, France 24 reported.
"There'd been no difficulties with him".
"He was someone who believed a lot in democratic ideals, the expression of free thinking, in journalism", Mercier said on BFM.
Neither the university president nor the thesis adviser mentioned the suspect by name. He said the man previously worked as a journalist for North African media. He was religious but had never displayed a hint of radical views, they said. "I think he started to take an interest in religion during his stay in Sweden", he told TSA-Algerie, a French-language Algerian site.
The attacker was working on a doctoral thesis in France.
Ikken's family is not religious, according to the nephew.
Mercier said he last saw Ikken in June 2016, and was surprised when his student failed to reply to his message in November saying they needed to arrange a meeting.
President Emmanuel Macron, portrayed by rivals as weak on security during the presidential campaign, ordered the task force to be set up last month to steer France's multiple security agencies from his Elysee Palace offices. The unit will focus on French citizens who joined the Islamic State group in Syria and Iraq.
Castaner said the attacker was not known by the police before the incident, adding that it "is very hard to anticipate" attacks when they were staged by people who were not on the police radar.
Aomar Ouali in Algiers, Algeria, and Lori Hinnant, Elaine Ganley and Sylvie Corbet in Paris contributed.