BRUSSELS — Belgium held a day of national mourning Friday for the 28 people who died in a school bus crash in Switzerland while Swiss authorities investigated whether the design of the tunnel contributed to the disaster.
Solemn music filled the airwaves in Belgium and official buildings dropped their flags to half staff. At 11 a.m, the nation of 11 million held a minute of silence to mark Tuesday's crash, which killed 22 children returning from "snow classes" in the Alps — a traditional rite of passage in Belgium from childhood to the teenage years.
Six adults — teachers, drivers and ski monitors — also died.
Trains and subways stopped in their tracks for the tribute, culminating three days of shock that slowly turned to heart-wrenching sorrow. Political leaders stood united in silence, factory workers briefly dropped their tools before Belgian churches slowly chimed their bells in unison.
Around noon, a long line of black hearses left a Brussels military airport to take the victims back to their home towns.
Peter Van Velthoven, mayor of Lommel where 17 victims lived, said the parents had gone through the whole gamut of feelings since Tuesday's accident.
"It went from disbelief to fear for the worst. Then hope that their child might have survived. Anger because the uncertainty took so long and then the fatal news, with its despair," Van Velthoven said.
The tourist bus carrying 52 people crashed head-on into a wall inside a tunnel as it headed home from a ski vacation in the Swiss Alps.
Olivier Elsig, prosecutor for the Swiss canton of Valais, said the crash is being investigated for three possible causes — a technical problem with the bus, a health problem with the driver or human error.
Investigators have so far determined it was a modern bus with two rested drivers and said the tunnel was considered safe.
But the Switzerland Federal Office for Roads said Friday it was examining whether the angle of the wall that the bus hit contributed to the severity of the crash. That part of the tunnel had a cutout for disabled vehicles, which meant part of the wall was at a right angle to the tunnel road.
"In principle there is the possibility of slanting the angle of the bay, or protecting it with concrete or other elements," spokesman Michael Mueller told The Associated Press.
But he cautioned that modifying the design of tunnel safety bays to better protect buses could have unintended effects for other vehicles, such as cars and motorbikes.
The tunnel where the crash occurred opened in 1999 and the German automobile club ADAC gave it the second-best of six ranking levels in 2005.
"Such a severe and tragic accident must always be taken as an opportunity to analyze the factors that could have influence the causes and effects of the disaster," said Mueller.
Many of the bodies were repatriated Thursday night and Swiss police said the remaining bodies were to fly home three Belgian military planes Friday.
Flags were lowered over the Belgian royal palace and in the Netherlands, too, government buildings flew flags at half staff. Six Dutch were among the dead.
During the morning rush hour in Brussels, workmen hung a Dutch flag half-staff at the country's European Union representation. The six Dutch kids who died in the crash attended school just across the border in neighboring Belgium.
One of the dead students was British, though living in Belgium, according to the St. Lambertus School in Heverlee, Belgium.
All EU flags hung at half staff along the EU Commission headquarters to mark the occasion.
At the KBC bank, automatic teller machines read: "We are speechless. All of KBC shares in the sorrow in silence."
Broadcasters rescheduled their programming, with VTM postponing the live finale of its popular singing contest "The Voice of Flanders" for a day.
Special ceremonies were held at the two schools that shared the bus bringing pupils home from their ski holiday. In Heverlee, the school gates, plastered with children's drawings about the tragedy, opened for the primary school kids to stand in silence before releasing white balloons up in the sky.
On Thursday evening, hundreds packed the Holy Cross Church in Sierre, the city in southern Switzerland where the crash took place, for a memorial Mass.
John Heilprin and Frank Jordans in Geneva, Jeffrey Schaeffer in Sion, Switzerland and Mike Corder in The Hague, Netherlands, contributed to this story.