Paris - What started as a hunt for two terror suspects grew into something worse - fears of a nest of terrorists that could strike again in the heart of Paris. The suspects in three attacks knew each other, had been linked to previous terrorist activities, and one had fought or trained with al- Qaida in Yemen - which claimed ownership on Friday of this week's newspaper massacre.Investigators are now trying to determine to what extent the attacks were co-ordinated.ManhuntThe Kouachi brothers had been the subject of a vast manhunt following the armed attack on the Charlie Hebdo weekly that claimed 12 lives on Wednesday. The brothers died on Friday when police attacked the building near Charles de Gaulle airport outside Paris where they had barricaded themselves.An acquaintance of at least one of the Kouachis, Amedy Coulibaly, 32, was identified as the suspected killer of a policewoman in suburban Paris the previous day - and as the man armed with a semi-automatic rifle who opened fire on Friday in a kosher market near Paris' Porte de Vincennes and barricaded himself with hostages there.He threatened to kill his captives if the Kouachis weren't freed. Like the brothers, he was killed when police moved in.According to French judicial documents obtained by The Associated Press, the connections among the terrorist suspects date back to 2010, when Coulibaly was sentenced to five years in prison for an abortive attempt to free another terrorist from prison. Smain Ait Ali Belkacem was serving a life sentence for a bombing attack on the Paris rapid transit system in 1995.Cherif Kouachi, 32, the younger of the brothers, was detained in that investigation, but freed later without being tried. A former pizza deliveryman, he appeared in a 2005 French TV documentary on Islamic extremism and was sentenced to 18 months in prison in 2008 for trying to join up with fighters battling in Iraq.The French judicial documents said Coulibaly and the younger Kouachi knew each another, and traveled with their wives in 2010 to central France to visit a radical Islamist, Djamel Beghal, who had been sentenced to 10 years in prison on a terrorism-related charge.Wife potentially ‘armed and dangerous’ Police issued a bulletin on Friday asking anyone with information about Coulibaly's wife, 26-year-old Hayat Boumeddiene, his suspected accomplice in the market attack, to contact them, saying she was potentially "armed and dangerous".According to the judicial documents, a police search of Coulibaly's residence in 2010 turned up a crossbow, 240 rounds of 7.62mm ammunition, films and photos of him during a trip to Malaysia, and letters seeking false official documents.In a police interview that same year, Coulibaly identified Cherif Kouachi as a friend he had met in prison and said they saw each other frequently, according to a transcript of the interview obtained by the Journal du Dimanche newspaper and posted on the newspaper's website.According to the newspaper, he told the police that people he met in prison used the nickname "Dolly" for him. He said he was employed as a temp worker at a Coca Cola factory."I know a lot of criminals because I met heaps of them in detention," he is quoted as telling the police.Michel Thooris, secretary-general of France's police labor union, told AP he didn't believe these were "three people isolated in their little world"."This could very well be a little cell," he said. "There are probably more than three people," he added, given that Cherif Kouachi and Coulibaly had had contacts with other jihadist groups in the past.Fears of new attacksFrench Prime Minister Manuel Valls, speaking in a TV interview late on Friday, also indicated authorities are bracing for the possibility of new attacks."We are facing a major challenge" and "very determined individuals," Valls said.The latest US assessments described to the AP show that the brothers led a normal life for long enough in recent years that the French began to view them as less of a threat and reduced the surveillance. They are continuing to investigate whether the brothers' steps away from radical Islam were part of a plan of misdirection, or whether it was real - and that they simply had another change of heart and decided to turn to violence.On Friday, a French TV news network said it spoke directly to Coulibaly before his death, and he said he and the brothers were co-ordinating and that he was with the Islamic State extremist group. BFM, the network, said it also talked to the younger Kouachi brother, who claimed to be financed and dispatched by al-Qaeda in Yemen, normally a rival organisation.Al-Qaeda in the Arabian Peninsula said on Friday it had planned the assault on the Charlie Hebdo newspaper staff - but did not mention the other terrorist acts.Trained with al-Qaeda in YemenSeparately, officials in Yemen and the US said Said Kouachi, 34, the older of the brothers, had trained with al-Qaeda in Yemen. Yemeni authorities suspect he fought with the Islamic extremist group at the height of its offensive in the country's south, a Yemini security official said on Friday.Another senior security official said Said Kouachi was in Yemen until 2012. Both officials spoke on condition of anonymity because of an ongoing investigation into the older Kouachi brother's stay.A US law enforcement official said on Friday that investigators believe Said Kouachi traveled to Yemen to receive weapons training from al-Qaeda. The official, who was not authorised to discuss an ongoing investigation by name, said the brothers had raised enough concern to be placed on the US no-fly list because one had traveled to Yemen and the other had been convicted of terrorism charges.Though the brothers claimed affiliation to al-Qaeda, the US official said, investigators were still trying to determine whether al-Qaeda had ordered the attack on the Charlie Hebdo offices or if the brothers had done it on their own.The official said investigators have been searching for any contacts that the brothers maintained with individuals in the United States, but had not yet found any.French authorities knew Kouachi traveled to Yemen, but it's not clear whether they knew what he did there, US officials believe. Still, French authorities placed both Kouachi brothers under close surveillance when he returned.