When something big happens there is a tendency to want answers. The most immediate quesition is "how could this happen?" Among those who believe in big government, mainly Progressives and big-government Republicans, the question becomes, "How could the government have let this happen?" This gives rise to conspiracy theories.
On the 50th anniversary of President Kennedy's assasination, the many conspiracy theories are being resurected. There is little to any of these. Most of them assume the coperation of the Vice-President, the Chief Justice of the Supreme Court, and leaders from both parties in Congress. The reasons given for assasination are even murkier. They mainly rest on the hope that Kennedy would have reversed himself on Viet Nam and withdrew troops instead of escallating and that vested interests were willing to kill him for this. This isn't even a stretch, it is preposterous.
The need to find meaning through government involvement can be seen in other tragedies. The 911 Truth movement was the same - people could not believe that something that big coud happen without the government allowing or even staging it.
Going back further we find debates about Franklin Roosevelt knowing about Pearl Harbor and allowing it to happen.
The sad truth is that terrible things happen and the government can't stop it.