PARIS (CBSNEWS) – Two days after the deadly coordinated terrorist attacks on Paris left at least 129 people dead and 352 injured, officials have begun to put together a picture of those responsible, and the arrests being made across Europe related to the attacks as well as the identity of those responsible are slowly being made public.

France has been in an official state of mourning since the attacks, with the Eiffel Tower going dark and President Francois Hollande vowing that France would wage “merciless” war on the Islamic State of Iraq and Syria (ISIS), which claimed responsibility for the mayhem, as investigators raced to track down their accomplices and uncovered possible links to networks in Belgium, Germany and Syria.

French officials have identified one of the Paris attackers as Ismael Mostefai, a 29-year-old Frenchman who had been flagged for links to Islamic radicalism. A French judicial official says Mostefai’s father, a brother, and several other people, including other family members, have been detained and are being questioned Sunday, French media report.

The mayor of the French city of Chartres, Jean-Pierre Gorges, identified Mostefai as a resident in a Facebook post. The judicial official confirmed the name, speaking on condition of anonymity because the investigation is ongoing.

The Paris prosecutor said Mostefai was identified by fingerprints on a finger found in the carnage of the Paris attacks Friday night. A U.S. law enforcement source told CBS News senior investigative producer Pat Milton French law enforcement officials were taking DNA and fingerprints from the dead terrorists. The test results were being run through databases as part of effort to identify the terrorists and their networks.

A neighbor in Chartres, Eric Pudal, said roughly 20 heavily armed police swooped in on the home Saturday evening.

Pudal said he was startled by the arrest, describing the family, which recently welcomed a baby daughter, as “very nice, very sociable.”

Pudal said he had never met the reported suicide bomber, Ismael Mostefai, and had never heard him being discussed by his neighbors.

Serbian police said Sunday the owner of a passport found near a suicide bomber in Paris entered the country on Oct. 7 from Macedonia – part of a wave of asylum-seekers crossing the Balkans toward Western Europe.

CBS News has confirmed the name on the passport is Ahmad Al-Mohammad. A U.S. intelligence source who confirmed the name warned however that the passport might be fake. The passport did not contain the correct numbers for a legitimate Syrian passport. Also, the picture did not match the name.

Police said in a statement Sunday that the man, identified officially only as A.A., formally requested asylum in Serbia. The statement says it’s the same passport holder registered as entering Greece on Oct. 3.

The Syrian passport was found next to the body of a man who attacked France’s national stadium on Friday night.

Officials in Greece say the passport’s owner entered through Leros, one of the eastern Aegean islands that tens of thousands of people fleeing war and poverty have been using as a gateway into the European Union.

Belgian authorities announced Sunday a total of seven people have been detained there in relation to the attack. Officials conducted raids in a Brussels neighborhood Saturday and arrested three people near the border with France after a car with Belgian license plates was seen close to the Bataclan theater. Molins said a French national was among those arrested.

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