Story and photos by CNN
In grainy images from surveillance footage, a man wearing light-colored clothes and a hat pushes a baggage cart through the airport.
It's one key piece of evidence authorities are looking at as they search for suspects after two explosions at the Brussels airport and another at a busy metro station in the Belgian capital Tuesday killed at least 30 people and wounded 230 others.
ISIS claimed responsibility for the coordinated attacks, but authorities said it's too soon to say for sure whether the terror group was behind the blasts.
So far, police have released photos of three men they say are suspects tied to the airport attack, standing side-by-side.
Two of the men, wearing black in surveillance images, are believed to be suicide bombers who died in the explosions in the airport's departure lounge.
But investigators believe the one in light-colored clothing planted a bomb at the airport, then left. Authorities called him a wanted man and asked for the public's help tracking him down.
"The third man left a bomb in the airport, but it didn't explode. ... And we are now looking for this guy," Belgium's Interior Minister Jan Jambon said.
A photograph released by investigators shows the three suspects side-by-side.
Federal Prosecutor Frederic Van Leeuw said the two men wearing black in the photograph were likely the suicide attackers.
Taxi driver tip sparks raid
A break in the investigation may have come from a taxi driver who took the suspects to the airport.
The driver contacted authorities after seeing surveillance footage and gave them the address where he picked the men up, according to two U.S. officials briefed on the investigation.
That information prompted authorities to raid a residence after the attacks, the officials said.
Investigators found a nail bomb, chemical products and an ISIS flag during a house search in the northeast Brussels neighborhood of Schaerbeek, Belgium's federal prosecutor said in a statement.
Hours later, they were still combing through the building for evidence.
Security was high. At one point, a helicopter hovered overhead, carrying a sniper with a weapon trained on the building.
As masked, armed officers stood guard outside the building, the burst of camera flashes inside could be seen from the street below. Officers left the building carrying bags of evidence they loaded onto vehicles.
Ties to Paris attacks?
A Belgian government representative told CNN that 10 people were killed and 100 wounded at Brussels' international airport. At least 20 people died and 130 were wounded at the Maelbeek metro station, officials said.
The blasts sent wounded people fleeing into the streets, spurred evacuations of nuclear plants and transit hubs and led to raids in some areas as authorities searched for suspects and evidence.