> Then Ulbricht walked into the public library and sat down at the table directly in front of me, and suddenly as I was reading I could look up and see exactly the chair he had been in, where the plainclothes police had positioned themselves, how they had arranged a distraction.
Alternately:
> Ulbricht had walked into the public library
gives the game away.
If you still want to play around a bit:
> I could see where Ulbricht walked into the public library. The table he sat at. I looked up and saw where the plainclothes police had positioned themselves, how they had arranged a distraction.
That way you are leaving some ambiguity, but are not directly lying with the tenses.
To go into the meat of this: he is imagining it while reading in the same location as the incident happened. This is a style of writing. It's definitely not wrong.