On the plane back to Washington, in her pink Chanel suit, caked with her husband’s blood, Jackie Kennedy resisted all suggestions from aides that she clean herself up. Instead, she just said, "Let them see what they’ve done."

But for the half century since John F. Kennedy’s assassination in Dallas on Nov. 22, 1963, the most famous artifact from that day, one of the most recognizable articles of clothing ever worn, has been seen by almost no one. Now preserved by the National Archives in a climate-controlled vault outside of Washington, it is subject to Kennedy family restrictions that it not be seen for almost a century more.

If there is a single item that captures both the shame and the violence that erupted that day, and the glamour and artifice that preceded it, it is Jackie Kennedy’s bloodstained pink suit, a tantalizing window on fame and fashion, her allure and her steely resolve, the things we know about her and the things we never quite will.

That Mrs. Kennedy is so closely linked to an item of clothing is fitting. In nearly three years as first lady, she had gained universal celebrity for her youthful style. Politically, it meant huge crowds whenever she accompanied the president. But for Mrs. Kennedy, who felt vulnerable, fashion gave her a sense of separation from the public’s gaze. It was armor.

So even on that day, before the horror of what ensued, to look at Mrs. Kennedy was to be drawn inevitably to the pink suit, a line-for-line copy of a classic cardigan-style Chanel with navy lapels. The suit came from Chez Ninon, a Park Avenue salon that created many of her clothes, following her taste for simple lines. She wore it at least six other times, including on a 1962 visit to London and that same year to greet the president of Algeria.

Fifty years ago, at noon in Dallas, Clint Hill, who was the Secret Service agent assigned to Mrs. Kennedy, thought the pink suit looked fluorescent against the dark blue of the car carrying the president and the first lady.

"She stood out so much in the car because of the color of that suit," said Hill, who has released a new account of the killing, "Five Days in November," in time for the anniversary. "It was like the sun just illuminated it."

Now preserved in its vault, the pink suit and its accessories, still stained, the stockings blood-powdered and folded in a white towel, remain essentially unchanged from the day of the assassination. Only the outfit’s matching pillbox hat and white kid gloves are missing, lost in the chaos of that day.

Although the National Archives has kept the suit and accessories, including navy shoes, bag and navy blouse, since 1964, when they arrived in a dress box, the items legally belonged after her death to Caroline Kennedy as her mother’s surviving heir. So a deed of gift was made in 2003 with the provision that the suit would not be seen by the public until 2103. Through her office, Caroline Kennedy declined to comment.

Over the years, the Kennedy family has sought to avoid the sensational treatment of assassination artifacts, and that is the explicit intent of the 100-year restriction. Nonetheless, Martha Murphy, chief of special access at the archives, said Jackie Kennedy’s clothes are the only items in the assassination collection with this specific restriction.

By comparison, scholars and researchers who meet special criteria of the archives may view President Kennedy’s clothing and the rifle used by Lee Harvey Oswald. To the best of anyone’s knowledge, access to Mrs. Kennedy’s suit for research purposes has never been granted.

After Mrs. Kennedy returned to the White House, early on Nov. 23, her clothing was put in a bag, presumably by her personal maid, Providencia Paredes, and soon after placed in a dress box. Records show that it arrived at the archives sometime before July 1964, accompanied by an unsigned note on the stationery of Mrs. Kennedy’s mother, Janet Auchincloss.

The note simply said: "Jackie’s suite and bag – worn November 22, 1963." It is unknown whether Auchincloss made the decision to send the clothes to the archives or, as many believe, was following her daughter’s wishes. Paredes, in an interview, said the suit was at first sent to Auchincloss’ home in Georgetown, but she is confident Mrs. Kennedy would have made the decision on where to send it. "Nobody would have made that decision for her," she said.

The Kennedy family never advised the archives about cleaning the suit, Murphy said, although leaving blood and other residue on garments is a standard conservation practice. "It’s part of the history of the object," said Phyllis Magidson, curator of costume and textiles at the Museum of the City of New York. Murphy, who has seen the suit, said it essentially looks brand-new.

For all Mrs. Kennedy’s visibility, it seems fitting that her pink suit should be hidden from view.

"She certainly understood invisibility and disappearance very deeply, as well as staged appearance," said the cultural critic Wayne Koestenbaum, author of "Jackie Under My Skin: Interpreting an Icon." "So the unseen suit is a very poignant and accurate emblem of her contradiction."

And noting that Mrs. Kennedy’s interest in historic preservation adds another facet to the suit’s status, Magidson said, "It has everything encapsulated within it."

Curators cannot think of another historical garment imbued with more meaning, and also deemed too sensitive to be shown. Among items of apparel with similar resonance are garments worn in concentration camps and the tatters that remained after the atomic blasts in Japan. But these objects, while deeply affecting, are displayed in museums. Other examples mentioned by curators include Napoleon’s death coat, a shoe dropped by Marie Antoinette on the way to the guillotine and the suit and cloak Abraham Lincoln was wearing when he was assassinated. Lincoln’s widow gave these items to a family friend. That man’s family kept them until the 1950s, when the American Trucking Association raised money to buy and donate them to the government. Since the ’60s, they have been on display at Ford’s Theater, though the cloak was put away because of wear.

But when Lincoln was alive, relatively few Americans knew what he looked like. Besides, his image, even if it had been familiar, would hardly have compared to Mrs. Kennedy’s riveting beauty and pop culture celebrity. She was, as Norman Mailer said in a 1962 essay critical of her televised tour of the White House, "an institution being put together before our eyes."

For that reason, combined with the fixation on President Kennedy’s assassination and a charged media culture, most experts believe that displaying her suit would be problematic. "It would produce hysteria if it were placed on view," Magidson said.

Those who knew her say it is almost certain that Mrs. Kennedy played a role in nearly every step of the suit’s journey from Manhattan dress shop to Dallas, and eventually to the vault.

She was a woman of meticulous organizational skills, who dictated to her White House secretary, Mary Barelli Gallagher, from her bed, and who dogged people with her morning memos. (Arthur M. Schlesinger Jr. once likened them to Churchill’s "Action This Day" memos during World War II.)

Gallagher’s 1969 memoir, "My Life with Jacqueline Kennedy" makes a good companion to "The Death of a President," by William Manchester, the one book on the assassination commissioned by the Kennedys. Loaded with details about Mrs. Kennedy’s work and personal habits, Gallagher’s memoir is sort of a backstairs view of the noble purposes that Manchester ascribes to her.

For instance, he referred to Mrs. Kennedy as a "retiring" socialite who was transformed by loss, "a new Jackie." But he did not consider that maybe the skills and determination that she used to hunt down clothes and furniture were the same qualities she magisterially deployed after the assassination.

And what about her stony refusal to change her clothes? Though describing White House duties, Gallagher offered many instances where Mrs. Kennedy had no compunction about saying no. She wrote, "If she didn’t want to participate in some activity, nothing could drive her to it."

The Manchester book described President Kennedy taking an unusual interest in what his wife planned to wear on the Texas trip, something he had never done in their marriage. He said to her, Manchester reported, "Be simple – show these Texans what good taste really is."

Paredes, though not disputing the account, gives less significance to it: "Maybe the president told her to wear the suit. I don’t think she gave it a thought. It was a practical suit to travel in."

She added, "I did pack a lot of clothes for her, because you never know about the weather. The president called me on the phone. It was the last time I spoke to him. He said, ‘You know, it’s going to be hot in Texas.’"

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Cathy Horyn, New York Times

© 2013 The New York Times Company