[echelon_musk]

Having rewatched that movie recently I found it absurd that all the killer would have had to have done to evade capture was purchase books with cash.

[badpenny]

Slight digression and spoiler alert, but, IIRC, wasn't it a significant part of the plot that he wanted to be caught?

[542354234235]

I'm going off memory, but I thought the library books led them to John Doe's apartment, something he was not planning for, and required him to change his plans somewhat. He did want to be caught, but not that soon, before he had finished his work, and required a hurried escape.