Bernice Moore posted something interesting on John Simkin's JFK Education Forum (see links) today:

From former Secret Service agent Marty Venker's book

"Confessions of An Ex-Secret Service Agent" , pages 24-25:

" [In Secret Service school] We'd also watch films of real-life
assassinations. Naturally, the featured attraction was the home movie Abraham Zapruder shot in Dallas on November 22, 1963.

THEY SHOWED YOU THE GRUESOME VERSION THAT THE PUBLIC USUALLY DIDN'T SEE, WHERE PARTS OF PRESIDENT KENNEDY'S BRAIN SPRAYED ALL OVER JACKIE. Again and again, I watched that film. The instructors didn't want us to ever forget it [Emphasis added]."