The texture of Capote's writing is compelling

I accept it is embarrassing how long I am spending reading this book. My defence is that there is plenty going on at the same time. The advantage is that there is an opportunity to savour after each short burst of reading.
I have just come through the part where Capote gives the texts of an exchange of letters between Perry and his sister plus a critique of the latter's writing offered by Perry's evangelical friend. These documents offer deep insights into Perry's character such that the reader is slowly nudged toward believing that Perry could have murdered. (I am not there yet).
The detective is not shown drink coffee and upturning clues, rather we are shown a view of the effect the investigation is having on his health and his marriage. This is deeply human stuff.
The problem with this is how on earth is the vital clue going to be uncovered. The answer comes in chapter 3 where the only person who can make the connection begins to do so and in a convincing way.