"Available evidence." That is a laugh. The bullet-hole riddled wall that the boy and his father crouched against was removed by the IDF.
And the cement barrel the father and child were hiding behind clearly took them out of the field of fire from the Israeli positions.
Furthermore the video clearly shows the father looking directly at the camera and shouting in that direction just before the fatal shots are fired whereas prior to that he was looking in the direction of the Israelis.
There are a number of other pieces of evidence all of which point to the shooter being alongside the camera man.
On the other hand what evidence can you present that it was Israeli fire that killed him?