Here's another article that presents some impressive facts supporting Mr. Donahue's theory.
"In Donahue’s first, the rifle jammed. In his second, he had trouble with the sticky bolt mechanism and only got off two shots, both of which hit. The third try was more successful. He was able to fire three shots, all of which hit, in 4.8 seconds. He later found that he was the only one of the eleven marksmen to better the target time. As a result of this test, Donahue was later approached by the editor of True magazine asking if he would write an article supporting the findings of the Warren Commission. He agreed, but asked for a little time to do his own research. And that was how it all started."
https://www.lindastratmann.com/news/26/438/Mortal-Error