I realised what was going on, but I did a double-take at:
> Then Ulbricht walked into the public library and sat down at the table directly in front of me
The problem is that two past events are being described, so tense alone cannot distinguish them. Cut the readers some slack; the writing could have been better.
Done for effect: it felt to the OP as if it was the present so the writing conveys that, while elsewhere making it clear the arrest was not the present.
To follow the tense and delivery of the previous sentence, it would have been clearest to say
"Then when Ulbricht..."
That "then" always does a lot of heavy lifting in English prose.
Yes, same here.