However in the United States Constitution the 10th Amendment states that all powers not explicitly delegated to the federal government are reserved to the states. Thus establishing the principle of the separation of powers between the federal and state governments as integral to American law.
Thus according to the constitution the role of the federal government is not that of an oversight body. I am anxious however to learn more on the subject if you can provide additional evidence that legally the role of the US Federal government is to act as an oversight body for the states.
EDIT: A lot of the replies have been informative, and well reasoned and there is a very compelling case from a legal perspective for the idea of the Federal government has the ability to compel local PDs in this respect. My hats off to the replies, very informative. I still don't know if the FBI would be the best appendage for doing something like this, but I do find the responses informative.
> No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws. [ ... ] The Congress shall have power to enforce, by appropriate legislation, the provisions of this article.
That gives ground for the US government to oversee the states, at least in matters of judicial and policing oversight.
The Federal government has the power to apply consent decrees to specific police departments when those departments are found to have used force excessively, per the 1994 Violent Crime and Law Enforcement Act[0]. This essentially opens police departments up to lawsuits if they exhibit a pattern of bad behavior. In fact, this law explicitly requires DOJ to issue an annual report on "the use of excessive force by law enforcement officers", although they haven’t.
0: https://en.m.wikipedia.org/wiki/Violent_Crime_Control_and_La...
Even if they don't have a legal right to do oversight, they can simply say you comply with this or you don't get federal money.
And when certain states broke off from the union and for a century continued to oppress the civil liberties of a race, the feds stepped in.
There is evidence of widespread abuse of police power and lack of accountability. There could be a Constitutional argument made about equal protection regarding a federal mandate on police oversight.
Update: Just to make clear I don't disagree that more data is good and that we should work to make all crime and police data available, but I don't think the FBI should be able to have absolute authority over local PDs.