On September 17, 1973, six days after the US-backed military takeover, Charles Horman was seized by Chilean soldiers and taken to the National Stadium in Santiago, which had been turned by the military into an ad hoc concentration camp, where prisoners were interrogated, tortured and executed. One month later, Horman's body turned up in a morgue in the Chilean capital. A second US journalist, Frank Terrugi, met with the same fate.

At the time of the military uprising, Horman was in the resort town of Viña del Mar, near the port of Valparaíso, which was a key base for both the Chilean coup plotters and US military and intelligence personnel who were supporting them. While there, he spoke with several US operatives and took notes documenting the role of the United States in overthrowing the Allende government. This discovery led to his secret arrest, disappearance, and execution. Efforts by his family to determine his fate were met with resistance and duplicity by US embassy officials in Santiago, who knew he was dead and why he had been killed.