Well, this is how they pinned down that troops in the Crimea were either Russian, or using Russian equipment.  

The unmarked but professionally equipped soldiers are almost certainly Russian "spetsnaz" units, according to Igor Sutyagin, a Russian military expert, who was imprisoned for several years by the Kremlin as a spy and is now a London-based analyst at the think-tank Rusi ...

Pictures of troops blockading Ukrainian facilities show them wearing izlom camouflage - obtainable in shops but used almost exclusively by Russian special forces. Many of the soldiers are also pictured carrying far more specialised kit: VSS Vintorez sniper rifles and NRS-2 knives, both standard-issue spetsnaz equipment.

If we can narrow down the weapons used that day at the end of February, that narrows the list of suspects. And it seems that there is widespread support on both sides for an investigation. By forcing both sides to wait for the results of that investigation, I think that you provide a context for things to de-escalate.

And I'll give my consent to any government that does not deny a man a living wage-Billy Bragg