A day after an Azerbaijani airliner’s crashed in Kazakhstan, aviation experts say the plane most likely went down after being hit by Russian air defense systems.

Russian aviation authorities said the Azerbaijan Airlines plane had hit a flock of birds. But some experts cast doubt on that account, pointing to footage showing apparent holes in the fuselage.

The Azerbaijan Airlines plane flew hundreds of miles off its scheduled route from Baku to Grozny, and crashed on the eastern shore of the Caspian Sea. Russia's aviation watchdog said a bird strike might have been the cause.