I'm not disagreeing that the placement was a bad idea, but it's tough (impossible) to catch everything. A major part of my job was the safety of others, both practically (preparing equipment to be worked on) and just talking about potential problems (process hazard analyses where you question every piece of equipment). It can be hard to question EVERYTHING. How far back do you go? If you need a firing range and find one available, do you automatically think to question it's validity? Most people will skip that step. "It's here, so it must be right." This tendency is exaggerated when put under pressure, say from time constraints. "We need to shoot this cannon. Well go get it done!!" It's not an excuse, but a reality. Examining the event after the fact makes it seem much easier. You already have the problems in front of you.
Safety will always cycle. Regardless of who and what you have in place (I can only speculate on their personnel) there will be a certain amount of complacency. With great people, procedures, and redundancies it will typically take longer to happen, more precise failures in a sequence to occur, or be less severe. There will always be an event to put you back on track.