I have always believed they were looking for evidence Trump might have taken with him proving Hillary and or Biden had committed crimes
I agree. Except for one thing… I suspect if there were incriminating documents in there that Trump had taken, I doubt that he knew about them.
But as Hillary, Biden, Comey, and Brennan probably knew (and I believe) there were quite likely documents that would indict them, and they wanted to get rid of every single last copy of those.
So they were willing to go to great lengths, even willing to expose getting caught to retrieve them. That’s what I think.