Several bombers are dead. At least one alleged attacker is still on the loose.
And a key question looms as investigators race to piece together details about the attackers behind Tuesday's deadly bombings in Belgium's capital: Were these men acting alone, or were other members of a terror cell supporting them?
Raids, arrests and forensic analysis are some of the tools investigators are using to get to the bottom of who was behind the attacks in Brussels, which killed 31 people and wounded 270 others.
Two of the bombers were brothers. And one of the bombers at the airport appears to be a man authorities named as a suspect in the Paris terror attacks.
But the investigation is far from finished. With at least one suspect on the run, the stakes are high, Belgian counterterrorism official Paul Van Tigchelt said Wednesday."There are still a number of people, possibly involved in the attacks still in our country ... who still pose a threat," he said.
Bombers were brothers
Belgian federal prosecutor Frederic Van Leeuw identified Ibrahim El Bakraoui as one of two suicide bombers at the Brussels airport and his brother, Khalid El Bakraoui, as the man behind a deadly suicide blast about an hour later on a train near the Maelbeek metro station.
his isn't the first time they've come across authorities' radar.
Ibrahim El Bakraoui was deported by Turkey to the Netherlands last year, a senior Turkish official told CNN. The Turkish presidency's office said authorities there captured him in June 2015 and flagged him to Belgian authorities.
Belgian authorities, the Turkish official said, responded in July 2015 saying he had a criminal record but no known ties to terrorism.
Van Leeuw offered a similar assessment of the brothers Wednesday.
"These two deceased suicide bombers had lengthy criminal records," he said, "but (were) not linked to terrorism."
Ibrahim El Bakraoui had been sentenced in October 2010 by a Brussels criminal court to nine years behind bars for opening fire on police officers with a Kalashnikov during a robbery, according to Belgian public broadcaster RTBF and CNN affiliate RTL.
Interpol had issued a "red notice" for Khalid El Bakraoui, the subway bomber, that noted Belgian authorities wanted him in connection with terrorism. But it wasn't clear when that notice was issued or why Belgian authorities now say he had no ties to terrorism.
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