At the same time new information has come to light about the apparent ease with which the plot's ringleader, Belgian-born Abdelhamid Abaaoud
, and others involved were able to get in and out of Europe.
Sources in France close to the ongoing investigation believe Abdeslam could not have survived a week on the run without help. They say that extensive raids in Belgium
on Sunday and Monday -- in which 21 people were detained in several locations -- targeted individuals suspected of a role in the network that organized the coordinated series of shootings and bombings that killed 130 people
in Paris on November 13.
Belgian Interior Minister Jan Jambon said Monday that "operations are not yet completed; they must be pursued."
Fifteen of those arrested
have since been released but one man has been charged with participating in the activities of a terrorist group and in connection with the attack in Paris.
Source: Abdeslam may still have suicide vest
Another man suspected of being part of the network is Belgian-born Ahmet Dahmani
, who was detained in the Turkish resort of Antalya three days after the Paris attack. A source close to the investigation told CNN that according to travel records Dahmani had travelled on a ferry on August 4 from Greece to Italy -- along with Salah Abdeslam.
A French source told CNN that officials feared a support network for the Paris attackers had not yet been dismantled and might be planning another attack, either in Belgium or France. The source said the presumption among investigators was that Abdeslam may still have a suicide vest.
Abdeslam was picked up in Paris hours after the attacks by two men who had driven from Brussels: Moroccan-born Mohammed Amri, 27, and Hamza Attou, 21. He had called them to say that his car had broken down.
Attou, according to his attorney, said he had found Abdeslam "extremely agitated and maybe ready to blow himself up," and was carrying "a big jacket and other things, maybe something like an explosive belt or something like that."
Late Monday, an article resembling a suicide vest was found in a garbage can
in the Paris suburb of Montrouge and was taken for explosive analysis.
Investigators say the suicide belts used by the Paris attackers appeared not to have been well-designed, nor to have had enough explosive to cause massive casualties. The vast majority of fatalities in the Paris attacks were caused by gunshot wounds, the source said.
Amri and Attou were arrested in Belgium the day after the attack and have been charged with terrorism offenses. Lawyers for the two men say they had no idea of Abdeslam's involvement.
One source told CNN that in the wake of the attacks and the intense Belgian investigation, it was suspected that a number of Belgian jihadists had left the country in an effort to reach Syria.
The hunt for Abaaoud
The source also disclosed further details of the hunt for Abdelhamid Abaaoud
, the alleged ringleader of the plot who was killed during the police raid on an apartment in the Paris suburb of St Denis last Wednesday.
It was only after the attacks that French security services became aware that Abaaoud, regarded as an influential figure among French and Belgian jihadists in Syria, had returned to Europe.
French Interior Minister Bernard Cazeneuve said that it was on November 16 -- three days after the attacks -- that "an intelligence service of a country outside Europe reported that they had been aware of his presence in Greece."
That country was Morocco.
At some point, surveillance video was reviewed from a Paris metro station near to where one of the attackers' cars was abandoned. It showed a man resembling Abaaoud entering the station.
But investigators still did not know where he had gone. Then they got a break. A female relative of Abaaoud -- Husan Aitboulahcen -- was under surveillance because she was suspected of involvement in an unrelated drugs trafficking case. Her cell-phone was the subject of a wiretap.
Monitoring her phone, investigators established she was in contact with Abaaoud and was going to meet him. A source close to the investigation told CNN the pair were photographed and tracked to the apartment in St Denis, which was placed under surveillance the day before the police raid in which Abaaoud and Aitboulahcen were killed.
Abaaoud 'visited Europe at will'
As investigators piece together Abaaoud's movements, an alarming picture has emerged of how he was able to evade detection for so long.
Sources close to the investigation say Abaaoud appears to have run a major conspiracy out of Greece at the end of last year. The plot involved multiple attacks being planned in Belgium.
In December 2014, Belgian police detected phone calls by Abaaoud from Greece to relatives of the conspirators. It's likely he called relatives in case the phones of the plotters were being tapped.
Belgian police moved against the cell in January; two of the conspirators were killed in a prolonged gunfight in the town of Verbiers.
It's not known how Abaaoud entered or left Greece, but he later boasted that he had managed to get all the way to Belgium.
"We faced a number of trials during the journey," he told ISIS' online publication Dabiq in February.
"We spent months trying to find a way into Europe ... we succeeded in finally making our way to Belgium. We were then able to obtain weapons and set up a safe house while we planned to carry out operations against the crusaders."
Sources in France say the evidence suggests Abaaoud then spent some time in Syria before coming back to Europe. In August, a man named Reda Hame was arrested on suspicion of planning a terror attack on a concert hall. When questioned by an investigating magistrate in Paris, Hame disclosed that he had met Abaaoud in Syria.
According to the French newspaper Le Monde, which obtained the interrogation transcript, Hame told investigators attacks were imminent.
"All I can tell you," he is reported to have said, "is that this will happen very soon. It was a real factory over there, and they are really trying to hit France and Europe. "
He was right.