As long as the USA maintains their "you are either with us or against us" attitude on geopolitics there can be no independent investigation. Recall that at the time of the Iraq "fake intel" WMD story, Bush junior was openly discussing that the US would reduce funding to the United Nations. Then the UN was strangely quiet about the illegal invasion of Iraq. 

It is no different now. All the global agencies are hostage to US money and allied voting blocks.