Europe

Swiss probe of fatal bus crash narrows to driver

  • Rescuers and police work amid the wreckage of a tourist bus from Belgium at the accident site in a tunnel of the A9 highway near Sierre, western Switzerland, early Wednesday, March 14, 2012. A bus carrying Belgian students returning from a ski holiday crashed into a wall in a Swiss tunnel, killing 22 Belgian 12-year-olds and six adults, police said Wednesday.  (AP Photo/KANTONSPOLIZEI WALLIS/POLICE OF VALAIS, Handout)  MANDATORY CREDIT

    Rescuers and police work amid the wreckage of a tourist bus from Belgium at the accident site in a tunnel of the A9 highway near Sierre, western Switzerland, early Wednesday, March 14, 2012. A bus carrying Belgian students returning from a ski holiday crashed into a wall in a Swiss tunnel, killing 22 Belgian 12-year-olds and six adults, police said Wednesday. (AP Photo/KANTONSPOLIZEI WALLIS/POLICE OF VALAIS, Handout) MANDATORY CREDIT  (AP)

  • Police and rescuers work at the wreckage of a tourist bus from Belgium at the accident site in a tunnel of the A9 highway near Sierre, western Switzerland, early Wednesday, March 14, 2012. A bus carrying Belgian students returning from a ski holiday crashed into a wall in a Swiss tunnel, killing 22 Belgian 12-year-olds and six adults, police said Wednesday. (AP Photo/Keystone, Laurent Gillieron)

    Police and rescuers work at the wreckage of a tourist bus from Belgium at the accident site in a tunnel of the A9 highway near Sierre, western Switzerland, early Wednesday, March 14, 2012. A bus carrying Belgian students returning from a ski holiday crashed into a wall in a Swiss tunnel, killing 22 Belgian 12-year-olds and six adults, police said Wednesday. (AP Photo/Keystone, Laurent Gillieron)  (AP)

  • A man places a flower tribute on a bridge near the entrance of the tunnel where a tourist bus from Belgium crashed on the motorway A9, in Sierre, western Switzerland, Wednesday, March 14, 2012.  Twenty-eight people, including 22 children, returning to Belgium from a skiing holiday died in a bus accident inside the road tunnel in Sierre in the Swiss canton of Valais, Swiss police said Wednesday. (AP Photo/Keystone/Laurent Gillieron)

    A man places a flower tribute on a bridge near the entrance of the tunnel where a tourist bus from Belgium crashed on the motorway A9, in Sierre, western Switzerland, Wednesday, March 14, 2012. Twenty-eight people, including 22 children, returning to Belgium from a skiing holiday died in a bus accident inside the road tunnel in Sierre in the Swiss canton of Valais, Swiss police said Wednesday. (AP Photo/Keystone/Laurent Gillieron)  (AP)

GENEVA -- Swiss authorities say they are narrowing their focus to the bus driver in a probe of a March 13 crash that killed 28 people, most of them children.

Twenty-two students returning from a ski holiday and six adults died when the bus crashed inside a tunnel in southern Switzerland on its journey back to Belgium. The 32-year-old driver was among the dead.

Prosecutors in the canton (state) of Valais said Friday their investigation has excluded the possibility another vehicle was involved, or that the road or tunnel were defective.

They also excluded speeding, alcohol or a technical problem with the bus as possible causes.

Chief prosecutor Olivier Elsig said in a statement that "from now the investigation is concentrating on causes linked to the driver of the bus."