In all cases it comes down to the shooters fault. The question becomes what are all the contributing factors, the chain of events leading up to the actual incident. Same thing in aviation accidents or other accident investigations. Many factors from health and state of mind of the individual, to equipment and its maintenance, required training obtained or not, trained habits, and often external factors like lighting, weather, exhaustion, distractions. So because a person says oh, my bad doesnt really explain the cause or exonerate the other factors involved.
When I person makes a obvious mistake it rests on the person who made it