As to which pilot would be at fault. In a 'formation' skydive, where two planes fly in formation before releasing the jumpers, it is the trail planes responsibility to maintain a position behind and above the lead plane. May have been a miscommunication as to the 'cut'. That's when the plane throttles back a little to allow the jumpers to climb out and exit. Lead plane may have 'cut' trail plane didn't and overtook as well as lost altitude, causing him to belly flop on the lead plane.