It's a huge gamble, but from what I'm reading the fear was further destruction of classified material that was taken from the White House when Trump's term ended.
That's the kind of thing that can fail regardless of whether this was a sound and sensible move or not. If stuff got deleted already, they were too late. If not, they have the evidence they need.
However, the optics of this are so crazy that I can't help but wonder if we're all missing some puzzle pieces. Because if the evidence just points to Trump taking classified documents, that's not even in the top 25 crimes for which he should be facing the music. But if the documents that were taken are specifically pertaining to discussions about Jan 6... Now that makes a wholly different story out of this.
I suspect we'll find out soon enough.