There was a peaceful protest, that was attacked by (pro-)Russian militants with guns. Then the crowd started to defend itself, the attackers retreated and barricaded themselves in a wooden building. They were still shooting into the crowd and throwing Molotov's cocktails. The crowd was was mostly unarmed save for it's own Molotov's cocktails.
Barricading inside wooden building and throwing fire around is not especially smart idea. That's how it ended, also.
Well, almost everything.