Attacks in Belgium’s capital killed at least 20 people at the Maelbeek metro station and at least 10 more at the international airport on Tuesday.
ISIS claimed responsibility.
Brussels was effectively locked down in the immediate aftermath. All flights were canceled, public transportation was shut down, and residents were told to stay indoors.
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 was a suicide bombing, according to Belgian prosecutor Frederic Van Leeuw.
The other remains under investigation.
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.
“It’s horrible,” baggage handler Alphonse Lyoura told CNN affiliate BFM, recalling a man who had lost both legs and other grisly scenes. “Belgium doesn’t deserve this.”
A bystander’s video captured the horror of the aftermath, with people motionless on the floor and dust hanging in the air, obscuring visibility.
Metro Station: About an hour after the airport explosions, another blast rocked the Maelbeek metro station toward the end of rush hour. The station is in the heart of the city, where European Union institutions are based, a symbolic target for terrorists. NATO is also headquartered in Brussels.
Strong winds rushed through the train car of passenger Sander Verniers as his train headed toward the station where the explosion occurred.
The train stopped in the middle of the tunnel, and then Belgian troops met the passengers as they disembarked from the train and walked along the tracks.
“We all had to get out,” Verniers told CNN. “There was a lot of smoke.”
Another bystander’s video depicted passengers stepping down from the cars in a dark tunnel, with a child crying.
The investigation
Suspects: Belgian authorities released an image of three suspects in Tuesday’s Brussels Airport attack.
Two of them carried out suicide attacks, and a third one is believed to have been a guide to ensure the other two would carry out the attacks, according to Van Leeuw and experts.
That third individual, dressed in a light jacket and hat, is being sought, the prosecutor said.
Information on suspects in the metro station attack wasn’t immediately available.
Raids: Police raids connected to Tuesday’s attacks were happening in the Brussels region, with authorities looking for people suspected of being linked to the deadly explosions, Belgian broadcaster RTBF reported, citing judicial sources.
Investigators were searching residences in connection with the investigation, but they weren’t saying where, Van Leeuw said.
At least one police helicopter with a sniper hovered over the Schaarbeek neighborhood as darkness fell Tuesday. The chopper apparently provided cover for raids unfolding 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.
Airport discovery: Belgian media reported a Kalashnikov assault rifle was found in the departure hall of the Zaventem airport.
Suitcase bomb? Investigators are looking at whether one of the airport explosions may have been caused by a bomb inside a suitcase, while the other was a suicide bombing, according to a U.S. official briefed on early evidence from the investigation.
This investigation is only just beginning and there’s much that’s not yet known, the source added.
Working theory about airport: Investigators suspect the attack was one of opportunity, targeting a large group of people in an area near airline ticket counters, two officials say.
There’s no indication so far the attackers tried to go past the security screening checkpoint, but investigators will have to do more investigation, including reviewing surveillance footage, to be sure, the officials say.
Authorities have yet to provide details on what they think the attackers’ strategy was at the train station.
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 about an attack in Brussels because there have been general concerns about terror threats, particularly in the wake of 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 traveled to join ISIS and other terror groups in Syria and Iraq. Many have been returning.
Global response
United States: “This is yet another reminder that the world must unite,” President Barack Obama said from Cuba, where he’s on a historic visit. “We must be together regardless of nationality or race or faith in fighting against the scourge of terrorism.”
France Security: France is deploying an additional 1,600 police officers around the country, French Interior Minister Bernard Cazenueve said Tuesday.
U.S. Security: At Washington’s Union Station, police were pulling random passengers, as they were boarding, to go through luggage security checks. ?Bomb-sniffing dogs were also out on the tracks doing sweeps.
Authorities in other U.S. cities, including New York and Chicago, are taking special precautions, like increased K9 sweeps of subways and additional police patrols.
The FBI is also boosting checks on the whereabouts of suspected extremists who are already being monitored and checking for any intelligence indicating possible threats in the United States, officials say.
Additionally, U.S. national security officials are on guard for possible copycat attacks, though there is no specific indication of any plots in the United States tied to the Brussels attacks, officials said.
Britain Security: British police have increased their presence at certain locations, including transport hubs like London’s Heathrow and Gatwick airports, according to Scotland Yard.
NATO Security: The alliance is raising its level of alert, it said in a statement.
