Najim Laachraoui, 24, is the latest suspect authorities have pinpointed in a web they say they're still trying to unravel.
Laachraoui's DNA was found in houses in southern Belgium and Brussels that the terrorists behind the attacks used, the Belgian prosecutor's office said Monday. Laachraoui traveled to Syria in February 2013, the office's statement said.
Since Abdeslam's capture, officials have said he was ready to carry out future attacks and supported by a wide network of associates, warning of the possibility of a new wave of ISIS terrorists preparing to carry out further strikes.
Laachraoui, who also has used the alias Soufiane Kayal, is considered dangerous and should not be approached, authorities said.
It's an alias investigators have mentioned before. They've previously said a man using that alias had traveled with Abdeslam and was in contact via phone with Paris attacks ringleader Abdelhamid Abaaoud, apparently giving him directives in the lead-up to the November attacks.
Prosecutor: Puzzle of attacks still unsolved
As they try to track down members of the terror network, police are also searching for Mohammed Abrini, a previously identified suspected accomplice of Abdeslam's who is believed to have driven him to Paris to carry out the attacks, for which the Sunni terror group ISIS claimed responsibility.
Paris prosecutor Francois Molins has said Abdeslam, 26, played a key role in planning the attacks in which nine terrorists killed 130 people with guns and bombs in Paris restaurants, shops and a concert venue the night of November 13.
But even with Abdeslam's capture, Belgian federal prosecutor Frederic Van Leeuw said Monday that the investigation still has a ways to go.
"We have a certain number of pieces of the puzzle, and some pieces have found their place," he said, "but we're far from having completed the puzzle."
Attackers' networks bigger than thought
Abdeslam's ability to remain at large for more than four months after the attacks and the apparent lack of information that authorities had on his movements have fueled concerns about the extent of the networks supporting the suspect.
Belgian Interior Minister Jan Jambon admitted to CNN on Sunday he was surprised that Abdeslam had been apprehended in Brussels, as authorities believed he had left the country.
"We don't know what he did for these four months. Did he stay in Brussels the whole time, or did he travel around?" he said, adding that the fugitive's support network was bigger than anticipated.
His comments were echoed by Belgian Foreign Minister Didier Reynders, who said Sunday that the investigation leading to Abdeslam's capture had shown more people were involved in the Paris attacks than previously thought.
"After the terror attacks in Paris, I said to one TV channel in the U.S. that we were searching for around 10 people with heavy weapons. We have far more than that since November, and not only in Belgium but also in France," he said.
"For the moment we have found more than 30 people involved in the terrorist attacks in Paris, but we are sure there are others."
Abdeslam's arrest had resulted in authorities recovering a large number of heavy weapons
, he said.
"He was ready to restart something in Brussels," Reynders said.
On Monday, a spokeswoman for the attorney general in the southwestern German city of Karlsruhe told CNN that Abdeslam had visited the town of Ulm a month before the attacks. The city is known as a stronghold for Islamists, some of whom are fighting for ISIS in Syria
Spokeswoman Frauke Kohler said she could release no further details while police investigate.
Lawyer: Abdeslam felt 'a form of relief' about capture
Abdeslam spent more than four months on the run as Europe's most wanted man before his arrest Friday. He's been charged with participation in a terrorist murder and taking part in the activities of a terrorist organization.
Abdeslam and his accomplice were traced to the residence where they were arrested after contacting an individual under surveillance by Belgian security services, a senior Belgian counterterrorism official told CNN. The two got in touch with this individual after escaping from their hiding place in the Forest district of Brussels during a gun battle with police Tuesday.
"We have significant coverage of known radical Islamist networks and he came right into our net," said the official.
The official also said Belgian police recovered a number of detonators from the Forest residence. It had previously been disclosed that weapons (a Kalashnikov rifle and ammunition) and an ISIS flag were found at the residence, but not explosives.
Abdeslam's attorney, Sven Mary, said in a radio interview Monday with Belgian state broadcaster Radio 1 that he believed his client felt some relief about being caught.
"I think that there was a form of relief, in the sense that the hunt was over," Mary said.
The lawyer, who met with his client Saturday, said he was cooperating with authorities and would eventually be transferred to France.
"There's not a single reason he wouldn't go to France. The only thing I wish for is to confirm the legality of the arrest warrant -- I think that is my job as lawyer. It is not a question of killing time not to go to France."
Mary had told Belgian public broadcaster RTBF on Sunday that he intended to file a complaint about remarks made by Molins, the Paris prosecutor, in which he had publicly disclosed at a news conference information that Belgian authorities had gleaned during his client's interrogation.
Molins had told reporters that Abdeslam told investigators that he had planned to blow himself up at the Stade de France, one of the targets of the attacks, but simply backed down.
However, the prosecutor said he was suspicious about that claim, reminding reporters that in a communique ISIS issued after the attacks, the terror group mentioned the commissioning of an attack in the French capital's 18th arrondissement, where none took place.
Abdeslam was known to have driven to the 18th after dropping off suicide bombers at the Stade de France.
Mary continued his criticism of Molins on Monday, saying: "We don't have a single lesson to learn from France. Period."
Other charges in Friday raid
Belgian State Security Chief Jaak Raes told CNN Belgian affiliate VTM News on Sunday that the threat posed to Europe by ISIS was far from over.
"We know that a number of people are possibly on their way to Western Europe, with the intention of conducting an attack -- to, with the 'jihad mentality,' do damage to Western democracy," he warned.
After the raid that captured Abdeslam, police charged Monir Ahmed Alaaj, also known as Amine Choukri, with the same crimes as Abdeslam. Alaaj was also wounded in Friday's gunbattle.
Three others were detained in the operation, one of whom was charged with participating in a terror group's activities and hiding criminals, and another with hiding criminals. The third was freed without being charged.