 One of the key props in the film is a diamond necklace. Because of  Robert Aldrich (qv)s insistence on accuracy, this was a real  diamond necklace, that came complete with a special female courier,  disguised as a secretary, and with an escort of guards on the set.  Special arrangements were made with the local bank and sheriffs  department in the location of Placerville, California, while the  necklace itself was transported by a motorcade of vehicles.