1) Any crime that requires the cooperation of two or more individuals is, by definition, a conspiracy. Since there are practical limits as to how much harm a lone individual can do, almost all of the greatest crimes in history were conspiracies, BY DEFINITION.

2) Occam's Razor suggests that for any crime, we investigate the simplest explanation first; and only if/when evidence rules that out should we go on to a more complicated one. Ironically, the simplest explanation for many crimes is that the 'victim' is also the perpetrator.

Consider arson. Who has the most obvious motive, means, and opportunity to set a building ablaze? Its owner, of course! (Assuming he has fire insurance, or by some other means can foist the cost of demolition and/or reconstruction onto other parties.) That is why a good arson investigator will always check out the owner's alibi first.

Similarly, whenever we see a crime so great that it significantly changes public attitudes and federal policy, the most OBVIOUS potential culprit is an element within government itself that desires just such changes, has the weapons to commit the crime, and the control over law enforcement to permit the crime to occur unhindered. Only if/when all relevant government elements have been exculpated should we investigate potential outsider criminals.