The mission was a sham. The murders were real.

Capricorn One

In order to protect the reputation of the American space program, a team of NASA administrators turn the first Mars mission into a phony Mars landing. Under threat of harm to their families the astronauts play their part in the deception on a staged set in a deserted military base. But once the real ship returns to Earth and burns up on re-entry, the astronauts become liabilities. Now, with the help of a crusading reporter, they must battle a sinister conspiracy that will stop at nothing to keep the truth hidden.