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Here’s what we know about the Brussels terror attacks

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Three explosions ripped through the Belgian capital of Brussels on Tuesday, March 22, 2016 killing dozens of people and wounding over 170 more, according to Belgian media.

Attacks in Belgium’s capital killed at least 20 people at the Maelbeek metro station and at least 10 more at the international airport Tuesday. Another 230 people were injured. ISIS claimed responsibility.

One person was arrested Wednesday in relation to the attacks, Belgian state broadcaster RTBF reported, but it was not immediately clear who the person was.

Authorities said earlier they had launched a hunt for a man who was shown in surveillance images at the airport wearing a light-colored jacket and black hat.

Two men seen alongside him in the surveillance images have been identified as a pair of brothers from Brussels, Khalid El Bakraoui and Brahim El Bakraoui, according to RTBF.

The brothers are the suspected suicide bombers who detonated explosives at the airport, a senior Belgian security source told CNN.

The city remains largely on lockdown, and the airport is staying closed Wednesday. Much of the city’s transportation system has been interrupted, although some services have resumed operation. Multiple countries, including the United States, United Kingdom and the Netherlands, are advising against travel to Brussels.

Here’s what we know:

The attacks

Airport: About 8 a.m. local time, two explosions struck the departure lounge of Brussels Airport in Zaventem.

One blast took place outside the security checkpoints for ticketed passengers and near the airline check-in counters, according to an airline official briefed on the situation. A bystander’s video captured the horror of the aftermath, with people motionless on the floor and dust hanging in the air, obscuring visibility.

A third bomb was left at the airport but didn’t go off, according to Belgian Interior Minister Jan Jambon.

Metro station: About an hour after the airport explosions, another blast rocked the Maelbeek metro station at the end of rush hour. The station is in the heart of the city, where European Union institutions are based, and is a symbolic target for terrorists. NATO is also headquartered in Brussels.

Bystander video showed passengers stepping down from rail cars in a dark tunnel, with a child crying.

Victims: The first victim to be identified is Adelma Marina Tapia Ruíz, who was killed in the attack at the airport, according to Peruvian state news agency Andina.

Originally from Peru, Tapia Ruíz had lived in Belgium for six years and was at the airport with her husband and twin 3-year-old daughters waiting to board a plane when the bombs went off.

The investigation

Suspects: Belgian authorities released an image of the three suspects in relation to the Brussels Airport attack.

The El Bakraoui brothers were known to police but for organized crime, not terrorism, according to broadcaster RTBF, which cited a police source.

One of them, Khalid, had rented a house at 60 Dries Street in the Forest municipality of Brussels under a false identity, which police raided last week.

The pair are suspected of having ties to the Paris attacks, a senior Belgian security source has told CNN.

The third, unidentified, man being sought is believed to have been a guide, charged with ensuring the others carried out the attacks, according to Belgian federal Prosecutor Frederic Van Leeuw and experts. He left the airport after accompanying the two. That appeared to be planned, the officials said.

There’s no indication so far that the attackers tried to go past the security screening checkpoint, but investigators are reviewing surveillance footage.

Belgian media reported a Kalashnikov assault rifle was found in the departure hall of the Zaventem airport.

Information on suspects in the metro station attack wasn’t immediately available.

Raids: Police raids connected to Tuesday’s attacks have been taking place in the Brussels region, RTBF reported, citing judicial sources, and one on Wednesday resulted in the arrest of an individual whose identity has not yet been released.

A taxi driver who took the suspects to the airport told investigators where he picked up the three men, prompting a raid in the area. He had recognized the men from the surveillance images, officials said.

Investigators were searching residences but did not disclose the locations, Van Leeuw said.

At least one police helicopter with a sniper hovered over the Schaarbeek neighborhood as darkness fell Tuesday. The copter apparently provided cover for raids on the ground, analysts said.

“During a house search in Schaarbeek, investigators found a nail bomb, chemical products, and an ISIS flag,” the federal prosecutor said in a statement.

The backdrop

“The Belgians have been sitting on a ticking time bomb,” one U.S. counterterrorism official said.

U.S. intelligence officials say they weren’t surprised by an attack in Brussels because there have been general concerns about terror threats, particularly after recent raids and the arrest of key Paris attack suspect Saleh Abdeslam last week.

Belgium has been a top concern for counterterrorism officials for years because of the large number of Belgian foreign fighters who have traveled to join ISIS and other terror groups in Syria and Iraq — more per capita than any other European Union country.

Many have been returning.

Last Friday, after more than four months on the run, Abdeslam was captured after being wounded in a gunfight with Belgium police in Molenbeek. Days later, Belgium and French authorities warned of more attacks.

After Tuesday’s attacks, Belgian officials raised the country’s terror threat warning to its highest level.

By Tiffany Ap and Tim Hume