What is the contention?
Police say that the same Isis (Islamic State) cell carried out the attacks on both Paris last November and Brussels this week.
What evidence is there?
European security officials said one of the suicide bombers was Najim Laachraoui, a Moroccan-born Belgian whom police have hunted as the suspected bombmaker in the November 14 attacks on Paris by Isis. Laachraoui's DNA was verified after samples were taken from remains found at the airport. Belgian authorities have been looking for Laachraoui since last week, suspecting him of being an accomplice of a suspected ringleader of the Paris attacks, Salah Abdeslam. A Belgian official working on the investigation told AP it is a "plausible hypothesis" that Abdeslam was helping to organise the Brussels attack.
What about the other bombers?
The other two suicide bombers were Belgian-born brothers, Ibrahim and Khalid El Bakraoui, both known to the police as common criminals, not anti-Western radicals.
However, Turkey says it warned Belgium and the Netherlands about Ibrahim when it deported him last year. Laachraoui, Ibrahim El Bakraoui and an unidentified man, who left a bomb in the airport but escaped and is still at large, were shown in airport video surveillance footage. Khalid El Bakraoui carried out a suicide bombing on the Brussels metro. Khalid El Bakraoui is believed to have used an assumed name to rent a Brussels area apartment where Abdeslam's fingerprints were found last week. Khalid was identified by his DNA in the attack on the subway. Ibrahim was identified by fingerprints recovered at the scene of the airport blast.
Any further links to each other?
Chief prosecutor Frederic Van Leeuw pointed to a rising sense of panic among the three bombers who blew themselves up. The prosecutor said a laptop seized from a rubbish bin on a street outside the brothers' last known address contained a message purportedly from Ibrahim El Bakraoui that indicated he was expecting to be arrested imminently following Saturday's capture of Abdeslam. "I don't know what to do, I'm in a hurry, people are looking for me everywhere," Van Leeuw quoted the message as saying. "If I give myself up I'll end up in a cell next to him," - an apparent reference to the just-arrested Abdeslam.
What physical evidence has been uncovered?
Inside the brothers' northeast Brussels residence police found an apparent bomb-making factory, including 15kg of homemade explosives and nails for use as shrapnel.
What evidence is there of Laachraoui's link to Paris?
Laachraoui is believed to have made the suicide vests used in Paris, a French police official told AP, adding that Laachraoui's DNA was found on suicide vests as well as in a Brussels apartment where they were made.
What are the authorities saying about the network?
French and Belgian authorities have said the network behind the Paris attacks - where seven jihadists blew themselves up or were slain by police - was much larger than initially thought. "It's the same team," said a French senator, Nathalie Goulet, who is co-leader of a parliamentary commission on studying jihadi networks. She said Abdeslam should have had little difficulty organising more recruits following his November escape from France. "He probably had 10 more at hand who would be ready to do the same thing tomorrow morning," she said, describing his Brussels acolytes as "like a scout troop .th.th. a troop of death."