The attackers were from Tajikistan, islamic. They were arrested in Briansk region, 100km from UA border. US ambacy gave warning to stay away from mass gatherings two weeks ago, and Victori Nuland warned that there are going to be nasty surprices some time ago. I don't see any doubt in who is the organiser.
Any surviver will be able to identify attackers, there are already plenty of videos online. And by the way UA ambassador to Tajik was recruiting fighters by his Tweeter account. Sick