Those observations, combined with interviews with rebel leaders, Ukrainian soldiers, and other research, indicated two things.
First, that until late on Sunday there were no rebel formations within about 30 km (20 miles) of the area where the armored column first appeared, and had not been for weeks beforehand.
And secondly, that before the armored column appeared, the area had come under artillery fire at times when the nearest rebel positions were beyond the range of most types of weapon that could have delivered the strike.
It was not possible to establish whether the people driving the column and firing the artillery were Russian soldiers or separatist rebels. But there were strong indications that whoever it was doing those things operated out of Russian territory - something very unlikely to have happened without Moscow's consent.
