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."  "We know these things can happen," she said, "but we must go on."  Both commuters declined to give their last names.  As Belgium mourned and Brussels struggled back toward some semblance of normality, new details emerged about the attacks.  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.  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.  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."  The Bakraoui brothers are suspected of having ties to  , 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.  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.  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."  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.  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.  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.  "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."  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."  CNN's Frederik Pleitgen reported from Brussels; Holly Yan and Catherine E. Shoichet wrote from Atlanta. CNN's Max Foster, Nima Elbagir, Joshua Berlinger, Nick Thompson, Arthur Brice, Evan Perez, Pamela Brown and Shimon Prokupecz contributed to this report.
Day broke Wednesday on a Brussels facing a new reality, and a new identity as a city contorted by grief but sustained by a shared determination to carry on.