I think they had a pretty good idea. All the presidential documents Trump took were illegal taken. They were government property. More disturbing were the missing classified documents that were in the custody of Trump or his staff. Knowing this, any AG would have done the same as Garland.
The most important thing is they got the stolen government documents including Top Secret classified documents back. I doubt Trump will every be prosecuted. He has been defrauding businesses, individuals, and governments all of his life and has never been convicted but at 76 years old, a reckoning is coming and it won't be too far off.