Evidence points to ...
Ukrainians? Perhaps, but too easy. Where's the intrigue in that?
Russian-speaking Ukrainians? Ditto.
Russian-speaking Ukrainians who support their twice-elected president and would prefer Moscow-rule to Kiev-rebels-backed-by-***-knows-who rule? Ummm ... ditto.
Actual Russians? Well, er, ditto once again. Why would they leave such an obvious trail?
The true expert agents provocateurs are here in the West, and have demonstrated readiness to joe-job anyone who opposes them. Even when they get caught they retain almost-plausible deniability (the "Gay Girl in Damascus" was a lone maverick, he had nothing to do with us, Guv).
Hmmm ... Where's Snowden?