When twin explosions hit Brussels early Tuesday morning, killing at least 31 people and wounding at least 270 others, they exposed a dangerous intelligence gap right in the heart of Europe.

Brussels, which is the capital of Belgium, also hosts the European Council, which represents the interests of the 500 million citizens who constitute the European Union.

Tuesday’s attacks—the first of which occurred in Brussels Airport and the second in the city’s metro station—came just days after authorities captured Salah Abdeslam, who is believed to be the last surviving member of the Islamic terrorist cell that carried out the November 2015 Paris terror attacks that killed 130 and wounded hundreds of others. 

On Tuesday, the Islamic State, also known as ISIS, claimed responsibility for both attacks, according to news reports.

Here we have four different security and counterterrorism experts give their takes on the failures that led to Tuesday’s tragedy and potential solutions that could prevent the attacks from happening again.  

Robin Simcox, The Heritage Foundation: Something ‘Quite Radical’ Needs to Be Done

Something “quite radical” needs to be done, Robin Simcox, a specialist in terrorism and national security at The Heritage Foundation, told The Daily Signal. The attacks, he said, “threaten the viability of the European Union project as a whole.”

The European Union project is the effort to unite nation-states together using a series of treaties, conventions, and agreements that encourage cooperation and discourage war.

Simcox said it’s too early to tell if the attacks were the result of a resource failure or an intelligence failure, but somewhere, he said, the system broke down.

“Did they have [the terrorists] on the radar and choose not to follow them, or are they not on the radar at all?” Simcox asked.

Simcox, who co-wrote “Al-Qaeda in the United States: A Complete Analysis of Terrorism Offenses,” a book profiling every known court conviction in America linked to al-Qaeda, said much of the blame falls on Europe’s “open border system,” which allows people to travel between countries with little to no security checkpoints.  

“The checks between countries are nothing like you would expect coming from the U.K. to the states or something like that,” Simcox said. “And that’s been a great asset for terrorists operating in Europe because after the Paris terror attacks, they were able to flee to Belgium and not be stopped.”

Europe’s “open border system” came as a result of the Schengen Agreement, which was signed in 1985 and went into effect in 1995. The majority of European countries, except the United Kingdom, have signed on to the treaty, which abolishes “all internal borders in lieu of a single external border.”

The treaty, Simcox said, predates the era of transnational terrorism and has now become a dangerous tool for terrorists.

“Not only are people not checked; there’s also the problem of checking them against various terrorist watch lists,” Simcox said. “I think the scale of the problem is too much. And the safeguards are insufficient.”

Complicating things further, Europe has become a “blurry mess” of values, Simcox said, sending mixed messages to refugees and immigrants on whether or not they need to assimilate.

“Europe needs to make clear what it stands for. Moments like this help clarify that, I hope.”

Belgian Counterterrorism Official: ‘It’s Very Grave’

From Buzzfeed:

One Belgian counterterrorism official told BuzzFeed News last week that due to the small size of the Belgian government and the huge numbers of open investigations—into Belgian citizens suspected of either joining ISIS, being part of radical groups in Belgium, and the ongoing investigations into last November’s attacks in Paris, which appeared to be at least partially planned in Brussels and saw the participation of several Belgian citizens and residents—virtually every police detective and military intelligence officer in the country was focused on international jihadi investigations.

‘We just don’t have the people to watch anything else and, frankly, we don’t have the infrastructure to properly investigate or monitor hundreds of individuals suspected of terror links, as well as pursue the hundreds of open files and investigations we have,’ the official, who spoke on condition of anonymity because he was not authorized to speak to the media, said.

‘It’s literally an impossible situation and, honestly, it’s very grave.’

Netherlands Counterterrorism Studies Professor: ‘A Bit Embarrassing’

What happened in Belgium is an embarrassment to the intelligence community, Edwin Bakker, director of the Centre for Terrorism and Counterterrorism at Leiden University in The Hague and a research fellow at the International Centre for Counter-Terrorism, said.

“It took them several months and this guy was not hiding on his own,” Bakker, who is also a professor of counterterrorism studies at Leiden University, told The Sydney Morning Herald. “That makes it a bit embarrassing for the intelligence community in Belgium.”

The “guy” Bakker referenced was Abdeslam, the Belgium-born suspect in the Paris attacks whom authorities arrested in Belgium last week.

“Apparently the intelligence position is not good enough to find these people or even to find the most wanted terrorist in Europe,” Bakker said. He added:

The events of today increase both worries about the intelligence position of Belgian authorities as well as how many supporters there are.

Problems and roadblocks to prevent terrorist attacks in Belgium stem from communication issues within the government, he said.   

“Belgium is a federal state and that’s always an advantage for terrorists,” Bakker told Reuters in November. “Having several layers of government hampers the flow of information between investigators.”

The Sydney Morning Herald reported:

Both Professor Bakker and Monash University terrorism expert Greg Barton [of Australia] said there was a strong chance that the Brussels attacks were carried out by extremists who were on the run after the Abdeslam arrest and decided they might as well launch the assault before they were caught.

Matthew Levitt, The Washington Institute: ‘Belgians Have a Really Big Problem’

“Belgians have a really big problem because they have the largest number per capita of western foreign fighters from any country,” Matthew Levitt, director of The Washington Institute’s Stein Program on Counterterrorism and Intelligence, told Business Insider. “The numbers are simply overwhelming.”

Belgium police have worked with French counterterrorism authorities but have “a problem both in terms of getting on top of the immediate threat that has developed over time” and putting in a plan to prevent Islamic radicalization, Levitt, a former U.S. intelligence and counterterrorism official, says.

Levitt was in Belgium last week meeting with counterterrorism and intelligence officials.

“The Belgians, over the past year, have been caught by surprise a bit that they are a target,” Levitt told The Washington Post. “That’s not a surprise anymore. I think the realization now is that the pace of the response has to be picked up significantly, and that has to be both raiding safe houses and getting into these neighborhoods and addressing the things that make people feel so disconnected.”