Exact details are sketchy and many of the anecdotal accounts of deaths that were reported by the commission that looked into the deaths came from highly suspect sources. For example, somewhere on the order of 400 out of 2,300 recognized deaths were members of the MIR - a marxist terror cell that specialized in car bombs and bank robberies.
What they did report though is interesting. 101 of the "victims" were shot attempting to escape from prison. 59 were convicted in military tribunals and sentenced to death. 93 were killed in "protests" (read: marxist thugs hurling rocks at Pinochet's troops). 90 were killed by private vigilante citizens. 39 were killed in gun battles with the police or military. 815 were allegedly executed in captivity. All of these people were deemed "victims of human rights abuses" by the pro-socialist commission that investigated them, even though many were clearly not (i.e. marxist thugs who were killed attacking the police) and some weren't even done by the Pinochet regime (i.e. the vigilantes).
Another thing to note - over half of the "victims" died during the coup and its 3 month aftermath in 1973.
Why kill any enemy once you have them under control?
Mostly because it was much more complicated than simply arresting them. Some of the "victims" died during the fighting of the coup, and in later gun battles with the police. Many of the "victims" were arrested first and ordered to leave Chile and never return, or else they would be executed. Pinochet followed through on his promise, and as late as the early 1980's they were still capturing marxist guerilla fighters in the jungles who turned out to be ex-Allendist officials who had returned from exile to agitate.
Nice run-down- Thanks.