Thanks for that Den.
I had not heard the sniper on the wall theory.
If that did happen, would the Paras believe the incoming fire was meant for them?
Re the 108 shots. If you fire a rifle at close range into a crowd you are boound to hit someone, and a single body would not stop a 7.62 high velocity round. 13 killed and 13 injured suggests only around 20 fired into the crowd. It could still be one out of control man. Others may have been attempting to return fire at real or imagined gunmen in the flats.
Something drove the Paras to take cover behind the low wall. they can be accused of much, but not nervous timidity.
Also there was a low velocity injury, and the brave priest saw an armed man in the crowd.

I realise this event is still painfull to many alive today, and fully accept that all the slain and injured were shot without any justification.