Perhaps just a conspiracy of silence involving KEY PEOPLE in all of those agencies and departments. The rest just do as they are told, see what they are allowed to see, say nothing out of fear of retribution, and otherwise have no voice.
If you don't believe this, then explain another case ... what happened in the crash of Ron Brown. In that case we know that the White House and Air Force leadership tampered with the normal investigation process. They skipped the Safety Board phase, which EVERY OTHER crash before or since has had. The Safety Board is the phase of the normal investigation process which is explicitly charged with "finding the cause". The final report from the Accident Investigation Board does not mention many facts that are highly suspicious ... such as the statements of the pathologists at the examination and what the x-ray of Brown's head showed. The final report also does not explain the loss of transponder and radio contact when the plane was 8 miles from the crash site, nor the coincidental "suicide" of the maintenance chief that was in charge of the beacon which disappeared just before the crash. It doesn't mention the fact that the Department of State was told there were two survivors ... not just one as was reported (a survivor who COINCIDENTALLY managed to die on the way to the hospital under a doctor's care after surviving for 10 hours on the ground). It also doesn't mention the apparent fact that the first rescuers to "officially" arrive at the crash site were met by 3 Americans on the ground (according to Associated Press). And the families (and lawyers) of the victims were also not told about any of the suspicious facts surrounding the crash. Instead the government paid out an average of about 14 million dollars per family to keep them from pursuing lawsuits (and thereby asking uncomfortable questions).
Further evidence that a few key people can control the flow of an investigation in the Brown case is that the White House and JCS ordered that there be no autopsy of Brown's body even though forensic pathologists at the examination called for one and every single pathologist to see the body or look at the x-rays since has said there should have been one. BY LAW, the FBI should have been called in once suspicions of gunshot were mentioned ... but they were not. The key department heads also have not investigated the disappearance of all photos and x-rays of Brown's head from a LOCKED safe at AFIP. Instead, they destroyed the careers of the military officers who did speak out, rather than simply show them that they were mistaken. They even threatened them with JAIL! That, of course, had a chilling effect on any other potential whistleblowers.
Since then, neither the FBI or military justice system has investigated even though there is clear proof that the management at AFIP lied to the public about the nature of Brown's injuries and the opinions of their pathologists regarding the need for an autopsy. They haven't investigated even though a military officer stated under oath that another officer told her that AFIP management tampered with a second set of x-rays to hide evidence of gunshot. They haven't investigated even though sworn testimony from one of Brown's close associates suggests a urgent motive for killing Brown at that time.
And that is just SOME of the evidence that exists pointing to the murder of Brown. There is additional testimony pointing to motive, opportunity and means ... all of which the key players in government have IGNORED or LIED ABOUT. And it doesn't hurt that the mainstream media is complicit. NOT ONE of the major media players EVER reported the facts of the Brown case to the public. Instead they just regurgitated the LIES spouted by the Air Force spokesperson and the Clinton administration officials about weather and blunt force trauma. Instead they just tried to associate those who question the Brown death with UFO-ologists.
So yes ... here is an example where a few key people have managed to keep the public from knowing the truth and controlled the investigation to the extent that suspicious evidence was buried or ignored. And if they could do it in this case, why think they couldn't do it in another?