Phil adopted the diary format because the editor wanted it that way. He wrote the book by going through newspaper microfiches, reading what the regular press had said about some events, recalling what really happened based on his own recollection, and putting it back together. I think most of the "how I wrote Inside the Company" is detailed in his follow-up book "On the Run," which is also a fascinating read. One thing to note about Phil is that his experiences have affected him and biased his judgement in some ways. He was there, and everything he writes is true, but he is an extremist, and often sees things in a bitterly stilted fashion, and sometimes does things that leads to the murder of US officials. One may argue that these officials engaged in oppresive operations and large scale murder are deserving of death themselves, as Agee does, but his "deserving of death" label has perhaps become a little too incompassionate.