DNA traces on an orange juice bottle and a surveillance video of a man praying in a mall led to the arrest Wednesday of a young suspected Islamic extremist accused of stabbing a French soldier patrolling a crowded area just outside Paris, officials said. 

The attack came days after a British soldier was slain on a London street in broad daylight, raising fears of potential copycat attacks.

The case also brought into question what authorities knew about the suspect, identified by police as Alexandre Dhaussy, because he had been tracked over several years. 

France has been on heightened security alert since its military intervention in January in the west African nation of Mali to oust Islamic radicals.

The French soldier attacked on Saturday is recovering from his injuries and has been released from the hospital.

The suspect was captured on camera offering a Muslim prayer in a corner of a busy shopping mall 10 minutes before he went after the soldier Saturday at the La Defense financial and shopping district, French prosecutor Francois Molins said Wednesday at a news conference in Paris.

The 22-year-old Frenchman bought the juice and the pocketknife used in the attack an hour beforehand, Molins said.

"The intent to kill is obvious. The suspect doesn't hesitate to stab several times with impressive determination," Molins said.

Suspect identified by DNA on juice bottle

The suspect was arrested Wednesday morning outside Paris at the house of a friend who hasn't been implicated.

"The suspect implicitly confessed when he told police 'I know why you're here,"' Molins told reporters. "The nature of the attack, the fact that it happened three days after the London attack and a prayer that was carried shortly before the attack make us believe that he acted in the name of his religious ideology and that his wish was to attack someone representing the state. "

Dhaussy, who was unemployed and homeless, was identified through DNA on a plastic juice bottle, said Christophe Crepin, spokesman for the police union UNSA.

The prosecutor said the suspect had converted to Islam around age 18. Authorities had his DNA profile on record after a series of petty crimes as a minor. 

'The suspect implicitly confessed when he told police "I know why you're here."'—French prosecutor Francois Molins

Intelligence officials operating in Yvelines, west of Paris, had tracked Dhaussy over several years. However, information gleaned on him, like his refusal in 2011 to take a job placing him in contact with women, never got bumped up to a national level, a statement by the French National Police headquarters said.

The statement said the acts, including his praying in the street in 2009, were "characteristic of fundamentalist behavior" that did not justify sending the information to the DCRI, as the national intelligence agency is known.

The police statement said the main mission of the DCRI where terrorism is concerned is tracking jihadists who uphold the use of violence, identify with al-Qaida, are active in internet jihad or sign up to fight abroad.

While looking for a job with a publicly-financed agency, Dhaussy did say he wanted to follow religious training abroad, the police statement said.

Under French anti-terrorism law, he can be held for 96 hours without charge.

Police will be investigating Dhaussy's internet searches, his travels and contacts to determine whether he acted alone or was part of a network, said Louis Caprioli, France's former top anti-terrorism official. 

"The early indications seem to suggest he acted alone," said Caprioli, now a security consultant at French risk management group GEOS. This would be the first time a French Muslim convert committed a lone-wolf style terrorist act, rather than as part of a terrorist network, Caprioli said.

Lone wolf attacks are the most alarming, Caprioli said, "because it's completely unpredictable."  

'Hundreds of potential Merahs'

"I have said before: There are dozens, if not hundreds of potential Merahs in our country," Interior Minister Manuel Valls told the iTele network, referring to Mohamed Merah, who carried out a series of attacks last year.

French security forces have been on heightened alert since the military intervened in the west African nation of Mali in January to regain territory seized by Islamic radicals. Yet even before the French military action in Mali, French soldiers were considered possible targets at home by local radicals.

Last year, three French paratroopers were killed by Merah, who police described as a French-born Islamic extremist. Merah went on to attack a Jewish school in southern France, killing a rabbi and three Jewish children in March 2012 before being killed later that month in a gunbattle with police. 

Intelligence authorities were roundly criticized in that case for tracking, then failing to follow up on Merah, even though he had traveled to Afghanistan and Pakistan.