Another snip (from the Forward section) of “The Death of a President” by William Manchester:
On February 5, 1964, Mrs. John F. Kennedy suggested that I write an account of the tragic and historic events in Texas and Washington ten weeks earlier. That is the first breath. The second, which must quickly follow, is that neither Mrs. Kennedy nor anyone else is in any way answerable for my subsequent research or this narrative based upon it. My relationships with all the principal figures were entirely professional. I received no financial assistance from the Kennedy family. I was on no government payroll. No one tried to lead me, and I believe every reader, including those who were closest to the late President, will find much here that is new and some, perhaps, that is disturbing. That is my responsibility. Mrs. Kennedy asked me but one question. Before our first taping session she said, “Are you just going to put down all the facts, who ate what for breakfast and all that, or are you going to put yourself in the book, too?” I replied that I didn’t see how I could very well keep myself out of it. “Good,” she said emphatically. And so I am here, weighing evidence and forming judgments. At times you may find my presence exasperating. You may decide in the end that I have been a poor judge. But you may not conclude that I have served as anyone’s amanuensis. If you doubt me you may as well stop at the end of this paragraph.
Actually, I discovered, the Kennedy family had not been eager to have any book written about the President’s death. Understandably they needed time to heal. But shortly after the burial in Arlington various writers solicited their cooperation in such a project. It soon became apparent that volumes would appear in spite of their wishes. Under these circumstances Jacqueline Kennedy resolved that there should be one complete, accurate account. I had not been among those who had approached her. (I had been living in the Ruhr, and was writing German history.) At that time I had not even met her. However, her husband had told her about me, and she had read a magazine profile I published about him the year before his death. Robert Kennedy also remembered my acquaintance with his brother. After consultation other members of the family agreed with Mrs. Kennedy that, in light of the fact that apocryphal versions of those days were already in press, it would be wise to have a book written by an author whom the President had known. It was further decided that the work should be based upon material gathered while memories were still fresh. Hence the invitation to me.
Apparently Manchester believed it was a bible. Here is what is in footnote 5 regarding it:
5 The myth of “the Catholic Bible” endures in Protestant America. Although such editions do exist, neither the obsolete (Douay) version nor the current (Confraternity of Christian Doctrine) rendition differs to any discernible extent from the one familiar to non-Catholics. Ecclesiastical scholars could distinguish between them, but Sarah Hughes couldn’t. Neither, in the opinion of Bishop Philip M. Hannan, could John Kennedy, and it is unlikely that the question had ever crossed the President’s mind.
Bugliosi in RH: "Author William Manchester wrote that JFK's Bible, 'his most cherished personal possession' was found on the plane, and LBJ rested his hand on it (Manchester, "Death of a President", pp. 324, 328). But Lady Bird took the "Bible" off the plane with her as a memento and later inquiry revealed it was not a Bible but a Catholic prayer book or missal which, to all appearances, had never been opened (Holland, "The Kennedy Assassination Tapes", p. 310)."
And here is Holland in "The Kennedy Assassination Tapes": "Manchester has his facts wrong, at least in this instance. The 'very personal' Bible belonging to President Kennedy - ostensibly the 'most cherished personal possession' - was in fact a Catholic missal or prayer book. To all appearances it had never been opened and it is not missing. Mrs. Johnson carried it with her as a memento when she disembarked at Andrews AFB."
The Holland book has a number of details on the events - some of which like above Manchester got wrong. It seems a lot of people were willing to say things later that they didn't want to in the immediate aftermath of the assassination. You might want to check that out in addition to Manchester's account.