PARIS (AP) -- 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 Friday of this week's newspaper massacre. Investigators are now trying to determine to what extent the attacks were coordinated. The 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 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 Friday in a kosher market near Paris' Porte de Vincennes and holed up 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. Police issued a bulletin Friday asking anyone with information about Coulibaly's wife, 26-year-old Hayat Boumeddiene, 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. French Prime Minister Manuel Valls, speaking in a TV interview late Friday, also indicated authorities are bracing for the possibility of new attacks. "We are facing a major challenge" and "very determined individuals," Valls said. Francois Molins, the Paris prosecutor, said authorities increasingly grew to see links between the attackers after they discovered that Boumeddiene and the companion of one of the Kouachi brothers had exchanged about 500 phone calls. Speaking to reporters late Friday, he said that 16 people had been detained in the investigation. Officials were continuing to look for "possible accomplices, the financing of these criminal actions, the source of these weapons and all the help that (the terror suspects) might have benefited from, in France as well as overseas, in Yemen," Molins said. The latest U.S. 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 coordinating 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-Qaida in Yemen, normally a rival organization. Al-Qaida in the Arabian Peninsula said Friday it had planned the assault on the Charlie Hebdo newspaper staff -- but did not mention the other terrorist acts. Separately, officials in Yemen and the U.S. said Said Kouachi, 34, the older of the brothers, had trained with al-Qaida 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 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.