Questions swirl over deadly crash of Azerbaijan Airlines plane. Here’s what we know

Azerbaijan held a day of mourning on Thursday for the dozens of victims of an airliner crash in Kazakhstan, as questions were being asked over the cause of the disaster.

The reasons that Azerbaijan Airlines flight J2-8243 came down are still unknown. Reuters reported Thursday that the plane was downed by a Russian air defense system, citing multiple unnamed sources in Azerbaijan with knowledge of the investigation.