Spoiler....
Was a direct reason ever given why they killed Charles 'Charlie' Horman? I just watched the film and I gathered that he knew too much about US involvement with the coup and the Chilean military was given the go-ahead to execute him. He was also keeping a diary of events that he had witnessed. Was this also a factor?
My other theory was he just got caught up in the chaos and they were killing people left and right with no hesitation. You spoke to the wrong person and you were dead. You kept a diary and you were dead. In other words, things got out of control very rapidly!
This was an excellent film and great performances. I read the book THE HOUSE OF THE SPIRITS (skip the film adaptation) and it gives a more Chilean angle on the coup. In the book, like the film, Chile is never mentioned by name.