(CNN) Dawn broke Wednesday on a Brussels facing a new reality -- a city contorted by grief but sustained by a determination to carry on.

And it was a day, of course, when the Belgian capital -- indeed, the European capital -- was more than ever acutely aware of its vulnerability.

Two explosions Tuesday at the city's main airport, and then another at a downtown subway station, killed 31 people and injured 270 others.

"You can feel the fear on the streets today," said Souheil, 21, who was taking the train Wednesday morning to his internship at the European Commission, near where the explosion at the Maelbeek metro station detonated Tuesday. "But you can also see that people want to fight it. It's a good thing."

A photo posted by Nick Thompson (@nickthompson88) on Mar 23, 2016 at 2:59am PDT

And Sarah, who is 20, sounded a similar note as she headed to school -- as usual -- in west Brussels on Wednesday.

"We know these things can happen," she said, "but we must go on."

Both commuters declined to give their last names.

Sarah, 20, is heading to school in west #Brussels today. Her friend's friend disappeared yesterday after the train attack at #Maelenbeek. "We know these things can happen, but we must go on." A photo posted by Nick Thompson (@nickthompson88) on Mar 23, 2016 at 2:41am PDT

As Belgium mourned and Brussels struggled back toward some semblance of normality, new details emerged about the attacks.

Prosecutor Frederic Van Leeuw identified Ibrahim El Bakraoui as one of the airport suicide bombers, and his brother, Khalid El Bakraoui, as the man behind the suicide blast near the metro station.

ISIS has claimed responsibility for the Brussels and Paris attacks -- raising concerns that the terrorist group is gaining more traction in Europe.

Mother ripped from children

Adelma Marina Tapia Ruiz was moments from boarding a plane to New York, where she and her family were looking forward to reuniting for Easter.

Adelma Marina Tapia Ruiz, 36, was among the vicims in the attacks.

Her husband and 3-year-old twin girls had just stepped away from the boarding area at the Brussels Airport. Then an explosion ripped the family apart, Peruvian state media said.

Ruiz, a Peruvian living in Brussels, was killed, reported Andin, a Pervian news agency. Her husband and daughters escaped serious injury.

The 36-year-old mother was one of at least 10 people killed at the airport. About an hour later, 20 people were killed at the Maelbeek subway station.

"We were fearing terrorist attacks," Belgian Prime Minister Charles Michel said Tuesday. "And that has now happened."

Brothers identified; manhunt underway

Brothers Khalid, left, and Ibrahim El Bakraoui are suspected in the attacks.

The Bakraoui brothers are suspected of having ties to the November terror attacks in Paris , which left 130 people dead. Khalid El Bakraoui rented a Brussels apartment that was raided last week, a senior Belgian security source told CNN.

The brothers were known to police for involvement in organized crime but not for terrorism, Belgian state broadcaster RTBF reported.

As officials try to learn more about the Bakraoui brothers, investigators are scrambling to find a third suspect believed to be at large.

Police are after the man on the right in connection with the airport attacks.

That man, shown in surveillance footage wearing a light-colored jacket and black hat, was seen pushing a luggage cart along with Ibrahim El Bakraoui and another apparent suicide bomber.

"The third left a bomb in the airport but it didn't explode," Belgian Interior Minister Jan Jambon said. "We are now looking for this guy."

Two people were arrested Tuesday in connection with the attacks -- one in Schaerbeek and the other in Haren -- though one of them was released later that day, Belgian federal prosecutor Frederic Van Leeuw said. Another person was detained Wednesday, according to Belgian state broadcaster RTBF.

A ghost city

Despite the determination to carry on, train platforms remained largely empty Wednesday save for a smattering of soldiers. People who did venture forth felt an eerie calm.

"Like walking through a ghost town," said 28-year-old Apelonia.

And as she rode the nearly empty metro into central Brussels, she kept imagining the train exploding and herself dying.

On the trains and in the streets, Brussels appears to be a city shaken yet defiant.

Lynn, who works at a communications firm, passed by Maelbeek station 30 minutes before the Tuesday's explosion.

"It's tough, but we knew it would happen," she said as she rode a replacement bus to work Wednesday.

"We have to go on," she said. "We can't stay home. We have to hope security can protect us."

Life in lockdown

About an hour after the explosion in the subway station, the city was virtually paralyzed, with most public transport shut down and residents terrified of more attacks.

Some metro lines partially reopened Wednesday, but the city's transit system announced that subway stations would be closed and the trains wouldn't be running from 7 p.m. to 7 a.m. Outside those hours, security forces are controlling all access to the stations.

Some cafes and shops in surrounding streets are still closed.

Military personnel, carrying automatic weapons and wearing scarves against the early morning chill stood guard in the area, where many European Union institutions are based.

Emerging from the chaos

Photos: World reacts to Brussels bombings Photos: World reacts to Brussels bombings Airport workers and their relatives in Brussels, Belgium, hold a candlelight vigil Wednesday, March 23, to pay tribute to those who were killed in terrorist attacks the day before. On Tuesday, explosions rocked the city's airport and a subway station. Hide Caption 1 of 23 Photos: World reacts to Brussels bombings Belgian national flags are projected onto the National Gallery in London's Trafalgar Square on March 23. Hide Caption 2 of 23 Photos: World reacts to Brussels bombings A woman in Brussels pauses after people observed a minute of silence at the Place de la Bourse on March 23. Hide Caption 3 of 23 Photos: World reacts to Brussels bombings Teresa Mancheno, a maintenance worker at Newark Liberty International Airport, attends a vigil in Newark, New Jersey, on March 23. Hide Caption 4 of 23 Photos: World reacts to Brussels bombings European Union flags fly at half-staff outside the European Commission in Brussels on March 23. Hide Caption 5 of 23 Photos: World reacts to Brussels bombings A young girl lights a candle at the Place de la Bourse in Brussels on Tuesday, March 22. Hide Caption 6 of 23 Photos: World reacts to Brussels bombings An image of the Belgian flag is displayed on the Trevi Fountain in Rome on March 22. Hide Caption 7 of 23 Photos: World reacts to Brussels bombings The Eiffel Tower is lit up with the colors of the Belgian flag on March 22. Hide Caption 8 of 23 Photos: World reacts to Brussels bombings Servicemen with Azov, a Ukrainian volunteer battalion, hold torches during a tribute ceremony at the Belgian Embassy in Kiev, Ukraine, on March 22. Hide Caption 9 of 23 Photos: World reacts to Brussels bombings U.S. President Barack Obama and his family observe a moment of silence as they attend a baseball game in Havana, Cuba, with Cuban President Raul Castro, right, on March 22. Hide Caption 10 of 23 Photos: World reacts to Brussels bombings A woman reads messages written on the ground at Brussels' Place de la Bourse on March 22. Hide Caption 11 of 23 Photos: World reacts to Brussels bombings A New York City church holds Mass for victims of the Brussels attacks on March 22. Hide Caption 12 of 23 Photos: World reacts to Brussels bombings A man places flowers outside the Belgian Embassy in Moscow on March 22. Hide Caption 13 of 23 Photos: World reacts to Brussels bombings A man looks at flowers and messages outside the stock exchange in Brussels on March 22. Hide Caption 14 of 23 Photos: World reacts to Brussels bombings Democratic presidential candidate Hillary Clinton, center, stands for a moment of silence during a roundtable with tribal leaders in Puyallup, Washington, on March 22. Hide Caption 15 of 23 Photos: World reacts to Brussels bombings A woman leaves a bouquet of flowers at the base of the Belgium and European Union flags, which were flying at half-staff March 22 at the Belgian Embassy in Washington. Hide Caption 16 of 23 Photos: World reacts to Brussels bombings Activists in Multan, Pakistan, condemn the Brussels attack on March 22. Hide Caption 17 of 23 Photos: World reacts to Brussels bombings A woman lays flowers at the steps of the Belgian Embassy in Berlin on March 22. Hide Caption 18 of 23 Photos: World reacts to Brussels bombings A boy at a makeshift migrant camp shows support for the victims near the village of Idomeni, Greece, on March 22. Hide Caption 19 of 23 Photos: World reacts to Brussels bombings Mayors of Istanbul districts walk with consuls from various countries, including Belgium, during a protest condemning terrorism on March 22. Hide Caption 20 of 23 Photos: World reacts to Brussels bombings People in Turin, Italy, take part in a rally to remember the victims on March 22. Hide Caption 21 of 23 Photos: World reacts to Brussels bombings France's Parliament observes a minute of silence on March 22. Hide Caption 22 of 23 Photos: World reacts to Brussels bombings Members of Quebec's National Assembly have a moment of silence on March 22. Hide Caption 23 of 23

The airport remained closed and will be shut down Thursday as well.

The country will observe three days of mourning, the Prime Minister announced.

And King Philippe and Queen Mathilde of Belgium will visit the Erasme Hospital in Anderlecht and the military hospital Reine Astrid on Wednesday, the royal household said in a statement.

'A ticking time bomb'

Belgium has been a concern for counter-terrorism officials for years because of the large number of Belgian fighters who have traveled to join ISIS and other terror groups in Syria and Iraq. Many have later returned home.

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

A Twitter post circulated by prominent ISIS backers Tuesday said, "What will be coming is worse."

The notion that the two suspected suicide bombers were known to authorities yet still carried out attacks shows how thinly spread intelligence authorities are, said CNN producer Tim Lister, who has reported extensively about terrorism.

"Even people like these brothers, who have criminal records, who have fired AK-47s at police, are still out there pretty much undetected," Lister said.

"It's estimated that just to follow one person 24/7 requires 25 officers or agents. There are just too many suspects to follow."

Photos: Terror attacks in Brussels An injured woman leaves the airport in Brussels, Belgium, after two explosions rocked the facility on Tuesday, March 22. There was also an explosion at a subway station in the city. Hide Caption 1 of 22 Photos: Terror attacks in Brussels Windows are blown out after the deadly attack at the airport. Hide Caption 2 of 22 Photos: Terror attacks in Brussels A police officer directs passengers in a smoke-filled airport terminal. Hide Caption 3 of 22 Photos: Terror attacks in Brussels Two wounded women are seen in the airport. Hide Caption 4 of 22 Photos: Terror attacks in Brussels This photo from inside the airport was shared by Jef Versele on Facebook. Hide Caption 5 of 22 Photos: Terror attacks in Brussels Subway passengers walk along the tracks following a blast at the Maelbeek metro station. Hide Caption 6 of 22 Photos: Terror attacks in Brussels A private security guard helps a wounded woman outside the Maelbeek metro station. Hide Caption 7 of 22 Photos: Terror attacks in Brussels Wounded people are treated outside the subway station. Hide Caption 8 of 22 Photos: Terror attacks in Brussels Rescue teams evacuate the subway station. Hide Caption 9 of 22 Photos: Terror attacks in Brussels Police officers guard the area around the subway station. Hide Caption 10 of 22 Photos: Terror attacks in Brussels People react as they walk away from the Brussels airport. Hide Caption 11 of 22 Photos: Terror attacks in Brussels A man with blood stains on his sweater leaves the airport. Hide Caption 12 of 22 Photos: Terror attacks in Brussels Passengers leave the airport after the attack. Hide Caption 13 of 22 Photos: Terror attacks in Brussels A young girl looks out of the window of a bus after airport evacuations. Hide Caption 14 of 22 Photos: Terror attacks in Brussels People stand near the airport after evacuations. Hide Caption 15 of 22 Photos: Terror attacks in Brussels Passengers gather outside the airport. Hide Caption 16 of 22 Photos: Terror attacks in Brussels Police officers stand guard near the Maelbeek metro station. Hide Caption 17 of 22 Photos: Terror attacks in Brussels A police helicopter flies above the area near the subway station. Hide Caption 18 of 22 Photos: Terror attacks in Brussels People embrace outside the Brussels airport. Hide Caption 19 of 22 Photos: Terror attacks in Brussels People are led away from the airport after the attacks. Hide Caption 20 of 22 Photos: Terror attacks in Brussels A victim receives first aid near the Maelbeek metro station. Hide Caption 21 of 22 Photos: Terror attacks in Brussels Ambulances arrive at the airport. Hide Caption 22 of 22

But the interior minister said Belgians refuse to be defeated.

"Our police services and our investigation services are very professional people, but we are also convinced that also the terrorists ... are professionals too -- and well-trained and well-formed," Jambon said.

"So it's a difficult battle against them. But I'm convinced that we will win."