When two white vapour trails cross the sky near the front line in eastern Ukraine, it tends to mean one thing. Russian jets are about to attack.
But what happened near the city of Kostyantynivka was unprecedented. The lower trail split in two and a new object quickly accelerated towards the other vapour trail until they crossed and a bright orange flash lit up the sky.
Was it, as many believed, a Russian war plane shooting down another in so-called friendly fire 20km (12 miles) from the front line, or a Ukrainian jet shooting down a Russian plane?
