There's little doubt that the FBI went in for something very important, that justified such an extreme call to action.
It's most reasonable to conclude that they got what they were looking for out of Trump's safe.
Their case against Trump has been well established by the Jan.6th. panel and now the incriminating on Trump's illegal activities is required.
Garland is demonstrating a surprising resolve to see it through for the sake of the country, even though the risks are becoming much bigger of the extreme right escalation to violence.
The streets of America are a tinderbox, ready to be set off by an extreme rightist committing a murder of a politician.