Images being widely shared on social media appear to show the train that has derailed in a mountainous area of Switzerland.
At least two carriages appear to have left the tracks and are hanging over a ravine.
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Police chief Kristen Ziman said that the officers were shot at as soon as they entered the Henry Pratt company building in Aurora.
The footballer had just signed for Cardiff City in a record transfer deal.
The 36-year-old was attacked in January.