In Brussels Bombing Plot, a Trail of Dots Not Connected

The stench of chemicals emanating from the sixth-floor apartment made the owner of the building gag. Other odd happenings at the mostly empty housing block in northern Brussels prompted an anxious resident in the area to alert the police. A taxi driver who picked up three young men at the block smelled a noxious odor leaking from their curiously heavy luggage as he drove them to Brussels Airport.

But not until 7:58 on Tuesday morning did these and other strange and, at least in retrospect, alarming dots come together to form a clear picture of what had been going on for more than two months in the dilapidated but spacious top-floor apartment at 4 Max Roos Street in the Brussels borough of Schaerbeek.

It was then that two homemade bombs — confected from malodorous and highly volatile chemicals in the living room of the apartment — exploded in the check-in area of the airport, followed an hour later by another at a busy subway station. Together, the attacks killed 31 people.

A third bomb was found unexploded at the airport, but the two that were detonated blew holes in the roof and maimed scores of people as they waited to check their baggage. On Saturday, the airport was still closed, a huge and macabre crime scene instead of a global crossroads and the main entry point to the “capital of Europe,” a city that houses the headquarters of the European Union and NATO.

Acting with uncharacteristic — and still unexplained — swiftness, Belgian security forces sealed off the area around the apartment in Schaerbeek within 90 minutes of the airport attack. The authorities attributed their speedy reaction to a tip-off from the taxi driver.

But the driver was said to have alerted the police only after a photograph of the suspects in the attacks was released hours later, raising questions about whether the police had perhaps already had the building in their sights but, for some reason, had not moved in and smashed through the front door to the sixth-floor apartment until it was too late.

“There were investigations before and after the events” of Tuesday, Alexandrino Rodrigues, the owner of the building, said in an interview, suggesting that the police had suspicions before the attacks and had not entirely ignored the report from a concerned neighbor. “You can’t catch a rabbit without knowing where it lives,” he added.

A small, idiosyncratic and proudly placid country, Belgium has none of the long and bloody entanglements in Muslim lands that have made the United States and neighboring France such obvious targets for global jihad. Yet with its large communities of often poor and poorly integrated Muslim immigrants and its own deeply rooted divisions of language, geography and politics, Belgium finds itself at the center of Europe’s struggle with terrorism and a glaring example of the obstacles blocking the way.

How the lengthy preparations for Tuesday’s attacks — by militants who either were or should have been on the authorities’ radar and, in some cases, with ties to the November attacks in Paris — could go undetected has stirred dismay and anger from politicians and also the public, as well as from allies in Europe and beyond.

“Why such repeated dysfunctions?” Marco Van Hees, a member of the Belgian Parliament, asked the Interior Minister and two other ministers who were summoned on Friday to explain the failure. “We are certainly not dealing here with just a glitch, a little bug, but a deep structural problem.”

How was it possible, members of Parliament asked, that two of the suicide bombers in the Brussels attacks, Ibrahim el-Bakraoui and his younger brother Khalid, both residents on Max Roos Street since the beginning of the year, had managed to go undetected for so long? And all this despite a record of violent crime in Belgium and, in the case of the older brother, a clear warning from Turkey in June that he was on his way back to Europe after being arrested as a suspected terrorist while on his way to Syria?

And was it really true, the lawmakers demanded, that the authorities had received a precise tip in December about the possible whereabouts of Salah Abdeslam, the only known survivor among the terrorists responsible for the Paris attacks, who was finally captured in Brussels on March 18? He was found at the address cited in the December tip-off, which had not been acted on because it had not been passed up the police chain of command.

In a sign the Belgian authorities had the Bakraoui brothers in their sights before they carried out their attacks, interrogators presented Mr. Abdeslam with photographs of the siblings after his capture and asked if he knew them. According to excerpts from the March 19 interrogation obtained by Le Monde, Mr. Abdeslam firmly denied knowing the men who three days later would subject Brussels to its bloodiest attack since World War II. The Belgians dropped the matter.

Whether Mr. Abdeslam knew about the attacks being planned for Brussels is still not known, but he certainly knew at least some of the militants who carried them out. The most notable was Najim Laachraoui, 24, who grew up in Schaerbeek and is thought by investigators to have run the bomb-making atelier on Max Roos Street and an earlier workshop on Henri Bergé Street where explosives were assembled for the Paris attacks.

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