When Said and Chérif Kouachi came to pray at their local mosque here in the suburbs north of Paris, they did so quietly and discreetly, saying very little. Except for the time the imam used his Friday sermon to urge worshippers to vote in a coming election.

"The older brother [Said] challenged the imam and walked out. He said it was not the imam's job to call on Muslims to vote," recalled Ben Ali, the head of the Ennour Association, which manages the Grand Mosque of Gennevilliers. "We respected his opinion and they left quietly."

Said Kouachi's refusal to take part in something as central to being French as voting in an election – and his apparent conviction that other Muslims should also boycott the democratic process – is just one of many tales that suggested the 34-year-old was heading in a direction radically at odds with the French state and society.

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There are other, darker stories told here about the two brothers who are the subject of a nationwide manhunt after they allegedly burst into the offices of the Charlie Hebdo satirical newspaper carrying Kalashnikov rifles Wednesday and began a shooting rampage that has left at least 12 people dead.

A neighbour in Gennevilliers told The Globe and Mail that she and her husband became so concerned about the behaviour of the Kouachi brothers – whom they could hear loudly reciting the Koran inside their apartment at all hours – that her husband and a friend decided to break in to the Kouachi residence when the brothers left to buy groceries. She said they found a "cache of arms" inside.

She said they were caught when the brothers returned home, and that they shoved her husband around and threatened him into silence. That was two months ago.

Before the attack, the brothers shared a fourth-floor apartment in Gennevilliers, a distinctly middle-class suburb on the northern fringe of Paris that counts a large enough Arab and Muslim population among its 40,000 inhabitants to justify a mosque big enough for 2,500 people to pray at once. Neighbours say Said and 32-year-old Chérif shared their apartment with a third man, named Mohammed, who was believed to be their brother-in-law, as well as a woman who always wore a head-to-toe jilbab, and tightly wrapped headscarf whenever she went outdoors. The woman rarely spoke to anyone but the men who lived with her.

Neighbours say police raided the brothers' apartment on Wednesday afternoon, several hours after the attack at Charlie Hebdo. A woman, whom French media reported was the wife of Said Kouachi, was taken into custody. Neighbours said the woman appeared to be heavily pregnant at the time of her arrest. Eight others were taken into custody Thursday in connection with the Charlie Hebdo attack. An 18-year-old, whose name had been linked to the attacks in the media, turned himself into police and reportedly told them he could prove he had been in class at the time of the attack.

"I'm scared they will come back and kill me for talking to you, me and my husband," said a middle-aged woman who answered the door next to the Kouachis' apartment at 17 rue Basly, a building midway between a very French bakery and a Middle Eastern kebab stand.

"Through the walls I could hear them praying all the time: 'In the name of God the most gracious, the most merciful. God is great.' My husband and a plumber forced the door open because we knew they were hiding weapons inside."

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The woman, a Tunisian immigrant who spoke only Arabic, said she didn't know what type of armaments her husband found inside the purple-doored Kouachi apartment. And her husband never warned authorities.

"They attacked my husband and pushed him against the fridge and said, 'Are you going to betray us to the police?'"

The answer was no, which partly speaks to the fear the Kouachis obviously instilled in their neighbours, as well as the chasm in understanding between French police and the Muslims who live in the banlieues of Paris.

That the Kouachis had been able to build up a store of weapons in their apartment half an hour's drive from the centre of Paris is startling, given that Chérif Kouachi is believed to have been on a security watch list. He was arrested in 2005 as he tried to board a plane to Syria, planning to go from there to Iraq to fight against the American army. He was convicted in 2008 of terrorism-related charges and sentenced to three years in prison. The second half of that term was suspended. Chérif was detained again – and his brother Said was named as a suspect – in a 2010 plot to break Smain Ait Ali Belkacem, the mastermind of a 1995 bombing of the Paris metro that killed eight people, out of prison. Police who searched Chérif's home found videos of al-Qaeda speeches and evidence on his computer that he frequented jihadi websites. Witnesses to the Charlie Hebdo attack say one of the gunmen claimed they were affiliated with al-Qaeda in Yemen.

At the Sahara kebab stand on rue Basly, customers and staff profess to have only known the Koauchis well enough to say hello. None claimed Thursday to be friends with France's most-wanted men, and many took pains to condemn their actions as barbaric and unrelated to the religion of Islam.

"These people are not Muslims to me. In the Koran it is written that whoever takes the life of a man takes the life of all humanity," said 20-year-old Sara Alan, an accounting student whose brother lived on the same floor as the Kouachis at 17 rue Basly. Her eyes welled with tears as she spoke.

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But there were others in the neighbourhood who clearly understood what might have motivated two residents of middle-class Gennevilliers to attack a symbol of the very different culture that surrounds them in France.

"You're asking the wrong questions," said a young African man who approached a journalist on the street outside the kebab stand. "You should ask yourself why someone would be willing to do this, why they would be willing to risk 20 years in jail … You should ask about the gulf in French society."

The Kouachis had far from a privileged upbringing – their Algerian-born parents died while both were young. French media reported Chérif grew up in an orphanage and, before his 2005 arrest, made a living delivering pizzas while he dreamed of being a rap star.

But in Gennevilliers, far from the poorest of the Paris banlieues, the gulf between Muslims and mainstream French society is less about economics than culture.

Mr. Ali, the head of the Ennour Association, said many young Muslims feel "humiliated" by a judicial system that prioritizes freedom of speech over freedom of religion, as well as an "Islamophobic" media that he says has helped pave the way for the rise of far-right politicians such as Marine Le Pen, who has occasionally topped opinion polls in recent months.

"Humiliation radicalizes and pushes people to extremes," Mr. Ali said "There is a minority [of French Muslims] who are not at ease, who don't want to integrate into the French milieu."

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Mr. Ali condemned the Charlie Hebdo attack as a "criminal, barbaric act that has nothing to do with Islam," and said he was happy to hear the newspaper was planning to publish as normal next week despite the carnage. But he hoped the paper would take account of the Muslim community it has so deeply offended.

"I want Charlie Hebdo to continue to work," he said. "Charlie Hebdo doesn't worry me. But I hope they will change a little the way they present Islam, and that they can understand that we can't laugh at everything. That there are limits to humour."

Illustrating the problematic relationship between France's police and its Muslim community, Mr. Ali said no officer had visited the mosque to ask about the Kouachi brothers after the attack.

Mr. Ali said the Gennevilliers mosque had received threats since the Charlie Hebdo shootings (there were explosions at two French mosques on Thursday, and Mr. Ali showed The Globe and Mail a tweet calling for French to arm themselves and attack mosques on Friday). But the mosque administration opted for unarmed lookouts on the street outside, rather than asking for police protection. "It's better for the community," he said.