The endpapers of this book are photographs of JD Salinger.

In the front he's young, in the army, at a camp table. This is actually a photograph of Salinger writing The Catcher In The Rye. In the back he's old, at a supermarket, standing in front of bags of charcoal. The journey from one photo to the other is pretty extraordinary. This is not a literary biography, but a companion volume to a documentary film. It's more a cabinet of curiosities than a book, with quotations from letters and from his family, friends, admirers and detractors. The comments of the compilers keep everything on track, admirably so, and by the end you wish that David Shields would write his own book on the subject.

JD Salinger was born in New York; his father was Jewish and his mother Catholic. Shields contends that, religiously at least, the wires were crossed from the beginning, but three things made Salinger, and broke him: the Second World War, the harsh faith of Vedanta, and Oona O'Neill.

Oona was the beautiful teenage daughter of Eugene O'Neill, seen in all the best places, even visiting the Stork Club after school. For a while she and Salinger were going out. He sent her long letters (as he did to every woman he was infatuated with, or wanted to infatuate).

One day she stopped writing back, and the next thing he knew she had married Charlie Chaplin. Even to a confident young writer-about-town, having your girl go quiet and then to find she's married the most famous actor in the world is pretty tough. He spent the rest of his life seeking girls who not only looked like Oona, but who were on the same shaky cusp of womanhood. He treated them terribly, interfering with their education, lecturing, hectoring and imprisoning them, really. God's gift to women.

The Second World War injured Salinger immeasurably; indeed the authors argue that he did not survive it, as a personality or as an artist. In 1941, America's entry into the war meant the sudden cancellation of his first short story in the New Yorker. Things got worse: Salinger served in two of the bloodiest engagements of the war, Hürtigen Forest and the Battle of the Bulge. He was present at the liberation of Paris, but also that of Kaufering IV, a death camp near Dachau.

A counterintelligence officer, he re-enlisted at the end of the war for a tour of duty in the "de-Nazification" programme. As for many soldiers with similarly shattering experiences, it wasn't going to be easy for Salinger to re-enter his old life, even if that was literary New York. "You never really get the smell of burning flesh out of your nose," he said once, "no matter how long you live." As if coming back wasn't going to be complicated enough, he brought home a German war bride as a present for his parents — and she may have been a Gestapo informant.

He began almost immediately seeking a way to make himself invisible, even terminal. Upon the publication of The Catcher In The Rye in 1951, he flipped. Unable to take the attention he was getting, he had his picture removed from the dust jacket, stopped reading reviews and vanished from the scene, holing up for the rest of his life in Cornish, New Hampshire, where he built a concrete "bunker" to write in. The choice of the word is apt, as Shields points out, because Salinger was bringing the war home for himself. And he brought it home to us.

The authors believe that The Catcher In The Rye is a disguised war novel, written in the throes of post-traumatic stress disorder. They explore the bitterness and underlying violence of its prose, and in one fascinating section trace the novel's role in the "kit" of several well-known assassins. (It's not Shields's and Salerno's fault, but almost no-one in this book seems to remember what a brilliantly funny writer Salinger is.)

After reading the Gospel of Sri Ramakrishna, Salinger became a follower of Vedanta. We are led to believe that he continued to write for years, concentrating on his fictional Glass family (to which his own families could never compare). He was writing about the Glasses in such a way as to disseminate the tenets of Vedanta.

Vedanta has a timetable for your life; it abjures contact with women and money. Salinger was always chasing women — he even "fell in love" with actresses on sitcoms, and he had a pile of money, so actually it sounds like he was a pretty lousy follower.

In the end Vedanta offers retreat from the world and then a passport to oblivion. This seems to have made him grumpier and grumpier. Obsessed fans would actually go to Cornish and knock on his door: one of the best parts of this book is some of the conversations he had with these people, who were, of course, the feeble fringe of his fan base. Most of them didn't have a coherent question to ask; it's as if they just wanted to gaze upon him.

And he got tired of this. To one, after asking if he was receiving psychiatric treatment (having just met him) he said: "Nothing one man can say can help another. Each must make his own way. For all you know, I'm just a father who has a son. You saw my son go down the road. I'm not here to help people like you with your problems. I'm not a teacher or a seer. I'm not a counsellor. I, perhaps, pose questions about life in my stories, but I don't pretend to know the answers." Unless you were a dark-haired, impressionable, literary young girl. Then he pretended to know the answers.

In case you missed the press coverage from the documentary release, Shields and Salerno claim to know something of what's in Salinger's famous "vault", as a result of spycraft it seems: at the least, they claim, there is a saga of the Glass family, mostly about Seymour and narrated by Buddy; there is a manual of the Vedanta religion with "fables" by Salinger; there is a love story of the Second World War; a novella in the form of a counter-intelligence officer's diary leading up to the Holocaust; and an expanded series of stories comprising a history of the Caulfields.

No publisher for any of these has been named, and Salinger's literary estate, which is run by his son Matthew, won't even confirm their existence.

This is an excellently done and useful book — it might even be called fun. Thrilling, at least. And, overall, it is a very disappointing thing to read about an author that so many wished so much for.

What could be more disappointing about JD Salinger than that he watched hundreds of hours of stupid television shows like Andy Of Mayberry or that he was a Republican? Either fact would support the idea he'd gone mad. The claim is that JD Salinger did exactly the wrong thing for himself, his readers and for art.

It is a solemn accusation, not comfortably made, one feels, and it sticks. From Cornish he ­micro-manipulated the "fact" of his reclusiveness, and everything else he could. It was, says Shields, "such an extreme lab experiment".

Despite being an inept Svengali, a predator on young women and a miserable, shell-shocked permanent adolescent who turned his back on New York for a life of paranoia and frozen peas, he was a gifted, multi-faceted artist who produced ground-breaking fiction that enthrals more readers every year. As Gay Talese said: "He was just a new man on the planet. And he carried us away."