It was likely to be yet another fruitless raid, the latest chapter in the agonizing four-month search for the terrorists who planned the attacks on Paris in November, the deadliest in Europe since the Madrid bombings of 2004. But it was anything but routine on Tuesday when Belgian and French police stormed into an apartment in Brussels’s quiet Forest neighborhood, a suspected terrorist safe house.

The apartment was not empty, as police had suspected it would be after records showed its basic utilities had been shut off for days. Gunfire erupted from inside, leading to an exchange that ultimately wounded four Belgian officers and killed a man later identified as Mohamed Belkaid, a 35-year-old Algerian with likely ties to the Islamic State. Two other men escaped.

But investigators found something else in the Forest apartment: the fingerprints of Salah Abdeslam, 26, the last known surviving participant in the Paris attacks. This was not the first time that traces of Abdeslam — who somehow had eluded Belgian counterterrorism police since November — had appeared. But it was the first time such traces led to the man himself, hidden away just over two miles from the seat of the European Union.

By Friday, authorities had tracked down Abdeslam, a French citizen but a Brussels resident, in the city’s predominantly Muslim Molenbeek quarter, wounding and arresting him and an accomplice in a raid on an apartment building there. By Saturday, Europe’s most wanted man was out of the hospital and cooperating with authorities, raising the prospect of long-awaited answers on both the November attacks and the gaping holes in Europe’s security system.

Dramatic video shows an ongoing police operation in Brussels linked to the deadly Paris attacks, with the sound of apparent gunfire and the capture of a suspect by police. (Reuters)

On Saturday afternoon, Belgian authorities officially charged Abdeslam with “participation in terrorist murder” and in terrorist activities. Hours later, the French Justice Ministry issued a new European arrest warrant that would expedite Abdeslam’s extradition and give the Belgians two months to transfer him onto French soil, or three if he appeals.

An appeal seems likely: Sven Mary, his attorney, told reporters here Saturday that Abdeslam plans to fight extradition to France, where investigators are eager to question a man suspected of being the logistics chief behind the worst terrorist attack in the French capital in generations.

Confirming what investigators had theorized since November, prosecutors also announced Saturday that Abdeslam had initially intended to commit suicide in the same way his brother, Brahim, had done in the Paris attacks. Brahim was buried Thursday in a quiet ceremony in Brussels, according to the Agence France-Presse news agency.

As security forces were celebrating their success in the Friday raid, new questions were being raised about a terrorist plot that may have been larger than investigators had believed. Belgium, for instance, has come under heavy criticism for failing to address radicalization within its own borders.

“The fight against the terrorist threat continues,” Belgian Prime Minister Charles Michel said Saturday after a meeting with top security advisers. Michel said that “between 300 and 400 investigators” had been working to track the fugitive in the months since he slipped out of the sight of authorities.

Emerging details about the raid suggested that the tip-off that led to Abdeslam’s capture may have been more luck than brilliant policing. According to a senior Belgian official familiar with the case who spoke on the condition of anonymity to discuss the ongoing probe, investigators also discovered that a phone number linked to Abdeslam at the time of the November attacks appeared to have been reactivated. They then traced it to the Molenbeek apartment where he was discovered Friday.

What we know so far about who carried out the Paris attacks

Security forces waited several days to raid the apartment because they were trying to capture Abdeslam alive, the official said.

Investigators believed that additional people were hiding in the Molenbeek apartment in recent days because residents there repeatedly ordered pizza in quantities far larger than would be needed to feed the people who were openly living there, the official said.

The apartment, on the rue des Quatre-Vents, is a short walk from Abdeslam’s family residence. On Saturday evening, a woman who answered a phone number that has been used to contact the Abdeslam family in the past said that she “absolutely did not” see Salah while he was in hiding. She did not identify herself and hung up.

The Molenbeek street where Abdeslam was captured was eerily deserted Saturday, and the gray-and-brown-brick building where he had been holed up bore no traces of the raid. A clerk at Boucherie Omar, a halal butcher shop across the street, said he was terrified that a key participant in the November attacks was found just a few hundred feet away.

“It’s a nightmare for us,” he said, declining to give his name. “He came, he went. We had no idea.”

Much the same was true in Forest, a sleepy enclave with a pet spa, bakeries and leafy parks where children played Saturday afternoon.

“I chose to live here because it was particularly calm,” said Georgiana, originally from Brazil, who witnessed the Tuesday raid from the windows of her apartment and spoke on the condition that her last name not be used. “Now,” she said, “it’s calm again.”

Belgian and French officials said they believed that Abdeslam’s capture marked a major success in Europe’s fight against homegrown terrorism, a problem that has surged with the expanding reach of the Islamic State, also known by the Arabic acronym Daesh.

Abdeslam’s arrest represents a “major blow to the Daesh terrorist organization in Europe,” French Interior Minister Bernard Cazeneuve said Saturday after meeting with other security officials at the Elysee Palace in Paris.

But leaders have also said the Belgian raids showed that even more people had been involved in the Paris attacks than they had at first thought.

And other observers questioned why it took Belgian counter­terrorism authorities so long to capture a man who may have been living in their midst for some time.

“Either Salah Abdeslam was very clever or the Belgian services were not. That’s more likely,” said Alain Marsaud, a member of France’s Parliament and a former counter­terrorism prosecutor, speaking on the Europe 1 radio station. Belgian authorities, he said, “watched this knot of terrorist vipers develop. They knew the danger.”

Birnbaum reported from Moscow and Mekhennet from Frankfurt, Germany. Griff Witte in London contributed to this report.

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