Investigation is a science. Science has a method. It works, independent of the most biased politicians. What one does with it is constrained by the science. As above, a rose is a rose.
I'll cut to the chase. The foremost scientists are not in the employ of the Public. "National", "Federal", "Bureau", "Agency".
I'm trying to think of an endeavour in which investigations are scrupulously honest, and the results therefrom are Truthful in expression.
No luck so far.