Doesn't look like it to me. Looks like whoever shot them checked the bodies for valuables, ID cards, etc, which would have meant turning them over. Notice their shoes have all been removed.
You're right. Plus, on further scrutiny, most of them have blood on the fronts of their shirts... blood wouldn't flow laterally or "up" if they were shot facing up. So they must have been shot facing down, and the blood flowed down onto the ground and soaked the front of their shirts.
This is such a sad sad tragedy. These poor guys... hearing their cohorts being shot one by one and knowing they were next. Animals did this, plain and simple.