GENEVA — Authorities say a bus crash last year in southern Switzerland that killed 22 Belgian schoolchildren returning from a ski holiday was probably caused by driver error or a fainting spell.

Six adults, including the driver in his 30s, also died in the crash on March 13, 2012.

Prosecutors in the canton (state) of Valais say a medical report concluded that the driver of the Belgian tour bus was suffering from a heart condition.

The report found the driver had also been taking antidepressants but these were unlikely to have triggered a suicidal impulse.

Earlier reports had discounted technical errors, speeding or alcohol as a cause.

Chief prosecutor Olivier Elsig said in a statement Tuesday that his office will now propose closing the criminal investigation into the case.