Who would have a motive for shooting down a Russian plane ?
Umm.. ISIS?
They are the ones claiming responsibility. And Russia did just launch a massive barrage against them.
The warnings given to German carriers only warned about flying below FL260 in the area of this flight and this flight was above that but anything's possible.
POTENTIAL RISK TO AVIATION OVERFLYING THIS AREA BELOW FL260 AND TAKE OFF / LANDING AT ALL AIRPORTS FROM DEDICATED ANTI-AVIATION AND GROUND TO GROUND WEAPONRY.