To be clear, the federal government can't *stop* local and state authorities from conducting their own investigation. They can just make it a lot more difficult by denying access to evidence, witnesses, etc.

1/6/21, 3:13 pm ET: President Trump tweets out that everyone at the Capitol should “remain peaceful” but does not tell them to leave the Capitol. The mob remains on the grounds.

1/6/21, 2:45 pm ET: Pro-Trump rioters invade the Senate Floor and break into Speaker Pelosi’s office.