Under our increasingly theoretical Constitution, the Federal Government has exactly ZERO policing powers within the “Several States”.
In extension, the DOJ has no legislative warrant to create a law ENFORCEMENT bureau.
Accordingly, since the FBI was simply created in 1908 and funded with existing funds, the Legislature \ever since\ has not agreed to nor codified the existence of the FBI as a law ENFORCEMENT mechanism capable of executing warrants, arrests and incarceration.
The Constitution has no language allowing any member of the Executive cabinet (branch) to muster and empower a law ENFORCEMENT group that has country wide authority.
But we have allowed it to go on for so long that it cannot be reversed.