During World War II, he served with the U.S. Navy, finishing with the rank of Lieutenant (Junior Grade).
Sprague served a year as photographic expert in the 1966-1969 investigations conducted by New Orleans District Attorney Jim Garrison.
[1] Five years later in September 1975, Sprague and L. Fletcher Prouty stated that their study of still photographs and film of the assassination revealed that no shots were fired from the Texas School Book Depository's sixth floor window and that Lee Harvey Oswald was framed by planted and altered evidence.
[3] According to Sprague's research, because of the location of the great oak tree with dense crown that crossed the trajectory of the shot from the 6th Floor of the building onto Elm Street, it is unlikely that Lee Harvey Oswald could fire from the window near where the rifle was subsequently found.
[4] Sprague's analysis of Abraham Zapruder's film was used in "The Guns of Dallas" article written by L. Fletcher Prouty.