[2][3][4] The investigation into the crash initially closed inconclusively in May 2013, having ruled out a number of factors that had been the subject of media speculation but failing to identify a cause.

[5] A further public investigation, closing at the end of June 2014, attributed the crash to a non-criminal error on the part of the coach driver.

[8] The crash occurred shortly after 9 pm local time (CET) on 13 March 2012, when the coach, while in the Sierre Tunnel, lost control, veered, slammed into a curb and then struck a concrete wall head-on, at the end of an emergency turnout area.

[16][6] Tests revealed the driver was not intoxicated with alcohol, did not suffer a heart attack or any other sudden illness, and prosecutors stated he was not exceeding the 100 km/h (62 mph) speed limit at the time of the crash.

[18] Police said that the coach, operated by Aarschot-based Top Tours, a company with an "excellent reputation", was a modern and well-maintained vehicle, and that the children had all been wearing the fitted seatbelts at the time of impact.

Peter Vanvelthoven, the mayor of Lommel, whose school lost 15 of its 22 pupils and both of the teachers aboard the coach, announced a memorial service the next week in the town, with attendees including the Belgian royal family and Prince Willem-Alexander and Maxima of the Netherlands.