You are being very naïve if you think Chilean legislature had no idea of the impending coup. As for the lack of evidence, I tried to find some and came back empty handed. If there were anything even distantly resembling the systematic use of violence Pinochet employed made by the Allende regime, I'm quite sure it would be amply documented by now, if, by no independent historians, by the Chilean military. Since I can't prove it didn't happen, do you have anything more solid than this to demonstrate it did?
Also your history is wrong; the document was used to justify 'impeachment' (because such a concept did not exist in the chilean constitution); the coup itself came afterwards, when Pinochet wrested his leadership of the military into overall civilian leadership, and I would not be so sure that the authors of the document intended the course of action that happened to be an indirect consequence of their petition.
The document, btw, passed the chilean legislature 81-47, which while not the two thirds required to remove the president, is still quite a supermajority.
Anyways, I think it should be the default assumption that governments torture people. There are scant few that haven't.