Wanted poster for Abdeslam Salah | Police Nationale The Belgian intelligence gap Brussels law enforcement authorities questioned, then freed two suspects in Paris attacks.

In the months before Friday’s terrorist attacks in Paris, Belgian law enforcement had identified some of the men who carried them out as radical Islamists. They had questioned and monitored them.

But they never detained them. Nor did the Belgians inform French authorities of their concerns.

The failure of Belgium to spot a plot that investigators now believe was in large part organized in central Brussels, or to flag information about known radicals to France, raises pointed questions about the country’s law enforcement and intelligence services.

It is already forcing a discussion in Belgium, as well as at EU level, about the way information is gathered and shared on potential terrorist activity.

Molenbeek links

Less than 24 hours after eight terrorists, working in three separate teams, used guns and explosives to kill 129 people in the French capital, police in Brussels carried out raids in the suburb of Molenbeek. At least four of the terrorists lived in Brussels.

At least three of them were known to Belgian police. Early this year, two brothers who allegedly carried out Friday’s carnage in Paris were questioned by Belgian authorities after one tried to travel to Syria, a spokesman for the federal prosecutors’ office said.

“We knew they were radicalized, and that they could go to Syria,” said Eric Van Der Sypt, spokesman for the Belgian federal prosecutor’s office. “But they showed no sign of possible threat. Even if we had signaled them to France, I doubt that we could have stopped them.”

Belgian security services had also been tracking Bilal Hadfi for months before the young man blew himself up at the Stade de France last Friday, sources at the federal prosecutor’s office and the justice and defense ministries told POLITICO Thursday.

“For several weeks, investigators put a tap on a house that was presumably the house where he was, but they didn’t find him,” said Sieghild Lacoere, the spokesperson for the justice ministry.

Belgian police had opened a case on Hadfi at the beginning of 2015 after the 20-year-old traveled to Syria.

“Belgium launched an international arrest warrant when he left,” said a spokesperson for the prosecutor's office, but authorities “lost track of him until he was identified in Paris.”

European security officials, speaking on condition of anonymity, said at least one of the Abdeslam brothers had traveled repeatedly between their home in Brussels and Paris in the weeks before the attack.

The older brother, 31-year-old Ibrahim Abdeslam — who blew himself up outside the Comptoir Voltaire café in Paris — “tried to go to Syria but he only got to Turkey,” said Van Der Sypt. Law enforcement didn’t detain him because “we didn’t have proof that he took part in the activities of a terrorist group,” he added.

“He was interrogated on his return, and his brother too,” said Van Der Sypt, referring to 26-year-old Salah Abdeslam, who is still on the run. It’s not clear if he tried to get to Syria.

Ibrahim Abdeslam denied that he had tried to travel to Syria, the prosecutor’s spokesman added.

Salah was believed to be hiding in the Brussels area, another Belgian official said Tuesday.

Missed signals

For Louis Caprioli, who ran French intelligence for 20 years and is now a consultant for security firm GEOS, the attacks in Paris expose the shortcomings in cooperation between national police and intelligence agencies across national borders in the EU that terrorists traverse freely. “Belgian authorities could have signaled to the French that these attackers would threaten France’s security,” he said.

Over the past two years, Belgium has experienced a spate of successful and foiled terrorist attacks. Last year a French gunman of Algerian origin killed four people at a Jewish museum in Brussels; in January this year, Belgian police killed two men in raids on an Islamist group in the city of Verviers; and in August, a man opened fire on a train from Amsterdam to Paris, after boarding in Brussels.

In all these cases, as well the Paris attacks, the suspects had links to Molenbeek, which Belgian police have raided several times since Saturday afternoon.

The older Abdeslam brother ran a café, Les Beguines, which had a rough reputation in the neighborhood and was closed down on November 4, nine days before the Paris attacks.

“There was a group of drug traffickers active in the café,” said Françoise Schepmans, the mayor of Molenbeek, who added that it was inevitable that “from such delinquency, it’s only a small step towards radicalization.”

Van Der Sypt, from the prosecutor’s office, said cooperation between Belgium and France was “very good,” but acknowledged that, with all the militants traveling to and from Syria, “Belgian police are already struggling to monitor these people 24/7.”

As a share of its population of 10 million, more Belgians have joined extremist militant groups in Syria and Iraq than citizens of any other EU state. About five percent of Belgium’s population is Muslim.

More than 130 Belgians who fought in Syria have come back, according to police and prosecutor sources. France and Belgium have task forces in each others’ countries to facilitate the sharing of information about terrorist activity, said Peter De Wael, spokesman for the Belgian federal police.

Belgian complications

Belgium’s unusual administrative and law enforcement systems complicate cooperation on counterterrorism with other countries. The country’s police is Balkanized along linguistic and regional lines. Its counterterrorism laws give authorites less latitude to investigate terrorism than in France.

“When I need to find the name of a car owner who is suspected of a crime, I need to send them a letter of request,” complained a senior Italian police official, speaking to POLITICO on condition of anonymity. “I only have these problems with the Belgians.”

The reckoning is starting. A standing government oversight committee on intelligence on Monday announced it would investigate the missteps that led up to the Paris attacks.

“You can expect in the next few days a fundamental review of how our intelligence services are working. We’re already working on it,” a Belgian official said.

“We don’t want to be shooting from the hip. There’s some work on what it should be. There’s a part of the budget being made available and people being made available. We’re working on how different services work together but that’s on an international level.”

By EU standards, Belgium’s civilian and military intelligence arms are small, even relative to its size. People familiar with these agencies also say they don’t have enough people who speak Arabic.

The organization of the police force is also coming into focus. Brussels has six different departments that cover 19 separate municipalities, each with their own mayor, which Interior Minister Jan Jambon says is one reason that the capital has an Islamist terrorist problem.

Any push by the federal government to centralize police control in Brussels faces local political resistance, which continued after the Paris attacks. Rudi Vervoort, who runs the Brussels region, said merging police zones is a bad idea, arguing the police need to get close to the communities it serves.

The law of the land

Belgian counterterrorism laws predate the rise of ISIL and the exodus of young Muslim men to Syria. The laws “were never designed to prosecute people going abroad to fight — they were only designed to combat terrorism domestically,” said Kris Luyckx, a lawyer who defended one foreign fighter in a trial this year.

Prompted by the shootout in Verviers this year, the government proposed 12 new counter-terrorism measures. It is now illegal to travel abroad with the intention of joining a terrorist group, and easier for security forces to tap the phones or electronic communications of suspected terrorists or recruiters.

“Privacy must sometimes yield to security,” said Brecht Vermeulen, who chairs the Belgian Parliament’s interior affairs committee.

Belgium still has a long way to go before its rules are as tough as those in France. French legislation on surveillance has been toughened up since the Islamist attacks earlier this year on the satirical paper Charlie Hebdo and a Jewish grocery store in Paris, in which 17 people died, though the law has not yet been fully implemented. French authorities can keep terrorist suspects in custody for up to six days without charging them — in Belgium, it is 48 hours.

“We thought that it wasn’t necessary, we know how to handle 48-hour custodies,” said Van Der Sypt, who described France’s anti-terrorism laws as more “severe.”

After every terrorist strike since 9/11 in Europe, most recently the Charlie Hebdo attacks in January, European countries have pledged to improve cooperation on policing and intelligence. Despite that, counterterrorism remains mostly a national matter.

“When it comes to European anti-terrorist policy, coordination does not exist,” said one senior European official, who asked not to be identified by name. “When it comes to security, it is 95 percent the responsibility of the member states.”

Police with borders

The one tool created to share information about wanted or missing persons — the Schengen Information System — “is not used in a systematic way by member states on our external borders,” said the senior Italian anti-terrorism official, who spoke on condition of anonymity.

Speaking at a POLITICO event in Brussels last week, Interior Minister Jambon said the exchange of information within the EU “isn’t always so obvious” but had improved a lot since the Charlie Hebdo attacks. Before then, four member countries were contributing information to Europol, the EU agency that coordinates the response to organized crime and terrorism. “Today, almost every country is contributing to the exchange of information,” said Jambon.

According to an internal document issued by European Council counter-terrorism coordinator Gilles de Kerchove, an excerpt of which was seen by POLITICO, 14 EU states, five other entities and Interpol have registered 1,595 people as foreign terrorist fighters on the Europol information system.

In the wake of the Paris attacks, calls are growing for an EU-wide response to ISIL terrorism. EU interior ministers on Friday will discuss possible measures, including better tracking of weapons and access to records of airlines’ passenger name records.

The ministers’ task could be made easier after the European Parliament civil liberties committee voted overwhelmingly last month to harmonize some of the existing national rules to help the fight against terrorism. The full Parliament will vote on their report this month in Strasbourg.

Security officials who push for improved coordination cite the case of Mehdi Nemmouche, the alleged 29-year-old perpetrator of the 2014 Jewish Museum attack in Brussels. A month before the attack, he arrived at a German airport, where he was stopped by German security. The Germans tipped off French intelligence — “but nothing happened and a month later the guy showed up in Brussels with a gun,” said the Italian police official.

Laurens Cerulus, Tara Palmeri and Hans von der Buchard contributed to this article.

This article has been updated.