He lived a long life, but took secrets to his grave. His account of what happened doesn't match the film evidence. At least he did acknowledge the head shot had a different sound.
There are lots of clips available. I don't think he kept anything secret. He always maintained that he jumped off the running board after hearing the first shot and sensing something wrong with the President. He did not hear the second shot but saw and heard the last shot. He believed that the second shot occurred while he was running along side the QM as that is what other agents told him - as documented by Gerald Blaine in his book "The Kennedy Detail". Blaine is still alive as far as I can tell.
Why do you think that does not match the film evidence?