NEW YORK >> It seemed self-evident at the time: A museum devoted to documenting the events of Sept. 11, 2001, would have to include photographs of the hijackers who turned four passenger jets into missiles. Then two and a half years ago, plans to use the pictures were made public.

New York City’s fire chief protested that such a display would “honor” the terrorists who destroyed the World Trade Center. A New York Post editorial called the idea “appalling.” Groups representing rescuers, survivors and victims’ families asked how anyone could even think of showing the faces of the men who killed their relatives, colleagues and friends.

The anger took some museum officials by surprise.

“You don’t create a museum about the Holocaust and not say that it was the Nazis who did it,” said Joseph Daniels, chief executive of the memorial and museum foundation.

Such are the exquisite sensitivities that surround every detail in the creation of the National September 11 Memorial Museum, which is being built on land that many revere as hallowed ground. During eight years of planning, every step has been muddied with contention. There have been bitter fights over the museum’s financing, which have delayed its opening until at least next year, as well as continuing arguments over its location, seven stories below ground; which relics should be exhibited; and where unidentified human remains should rest.

But nothing has been more fraught than figuring out how to tell the story.

SIFTING THROUGH PAIN

As the former associate director and a 19-year veteran of the U.S. Holocaust Memorial Museum in Washington, Alice Greenwald knows a lot about ghastly things. Yet even that museum did not have to wrestle with the challenge of being built where the horrors had occurred and while the families of victims were still grieving.

Since being appointed director of the Sept. 11 Museum in 2006, Greenwald has inherited much of the distrust some of the families feel toward officials involved in developing the site, particularly Mayor Michael R. Bloomberg, who at one point said that if he were a mourner, he would “suck it up and get going.”

In particular, many families are upset about a plan to place approximately 14,000 unidentified or unclaimed remains of those who died — typically bone fragments or dried bits of tissue — in the museum below ground. The repository will be controlled by the city’s medical examiner and sealed off from everyone but family members. Visitors will just see an outer wall inscribed with a quotation from Virgil: “No day shall erase you from the memory of time.”

Seventeen family members have filed suit against the city as part of an effort to reopen the decision. They view it as degrading to set the remains in a museum below ground. Rosaleen Tallon, whose brother, Sean, a firefighter, died in the north tower, said the insensitivity was mirrored in the museum’s decision to stock its gift shop with $40 souvenir key chains engraved with the Virgil phrase.

“They’re marketing the headstones of our loved ones on key chains,” she said. “How disgusting is that?”

But to Greenwald, the decision to keep the remains underground represented an equally earnest effort to fulfill a longstanding promise to other families who had sought, above all, to ensure that the remains stayed at bedrock.

“It’s been a very difficult, fascinating and challenging process” to juggle competing visions of what the museum should be, she said.

Throughout, Greenwald reached out to the varied constituencies by inviting some of the most influential and outspoken players to assist the museum’s board. It was led by Bloomberg and included the first deputy mayor, Patricia E. Harris. Among the 11 family members on the roster was Debra Burlingame, who lost her brother, an American Airlines pilot, in the attack on the Pentagon.

Greenwald drew in an even wider circle by holding a series of discussions about topics like exhibiting disturbing material and handling human remains. It was an exhausting process, with dozens of conversations that solicited the opinions from survivors and family members of victims; residents and business, community and government representatives; and uniformed rescue and recovery workers among others.

As the conversations continued, a subtle map of divisions surfaced that ran along class, geographic and political lines: New Yorkers found outsiders meddlesome; families of uniformed rescue workers were resentful of Wall Streeters’ moneyed influence; critics disdained those willing to compromise.

Civil War historian David Blight, who served as an adviser to Greenwald during the process, said the overriding question for him was what message visitors would take away: “Are they going to leave with any sense of why this happened and its consequences? Or will they be moved solely by the sheer power of the catastrophe? If it’s only the latter, then the museum is a failure.”

DIFFICULT DECISIONS

Everyone agrees that it is the museum’s job is to tell the truth. The question, though, is how much truth.

The museum has more than 4,000 artifacts, from a wedding band to a 15-ton composite of several tower floors that collapsed into a stack, like pancakes, and then fused together. There are photographs of men and women jumping out of windows, burned and mutilated bodies, scattered and blood-soaked limbs, images so awful they tested the bounds of taste and appropriateness.

There are thousands of harrowing first-person recollections, and photographs and videos from survivors and witnesses, many of them raw. Many victims’ final phone calls were preserved. Flight 93’s cockpit recorder captured the hijackers’ last words and a flight attendant’s begging for her life.

Which of it should be on display?

“We have to transmit the truth without being absolutely crushed by it,” Daniels, the chief executive, said. “We don’t want to retraumatize people.”

Within months of settling into her office at 1 Liberty Plaza in Lower Manhattan, Greenwald invited Brady P. Gray, a disaster psychologist who consulted with the Fire Department after Sept. 11, to speak with the staff and advisers. He explained that hearing a recording could be more disturbing than seeing an image because it requires more imagination.

“The mind is left to create the illusion of what was taking place,” Gray said. “We personalize things that we don’t see so well.”  Over time the team pulled back further from exhibiting graphic carnage. Curators followed a guideline used by the Oklahoma City National Memorial & Museum, which commemorates the 1995 bombing of the Alfred P. Murrah Federal Building by Timothy McVeigh that killed 168 people. “We don’t show body parts, but we show blood,” Kari F. Watkins, that museum’s executive director, said in an interview.

Greenwald explained that there were other ways to convey horror, as when it is reflected in the faces of witnesses. “The historical reality is that there were body parts littering Lower Manhattan,” she said. “We do not feel the need to display that.” Particularly upsetting items drew additional review by the program committee, as well as by advisers and staff. Opinions about whether to include images of trapped victims leaping from the flaming towers were mixed. The New York City fire commissioner, Salvatore J. Cassano, who was involved with the discussions, was opposed.

“I didn’t think it was respectful to show people jumping out of windows,” he said.

After repeated discussions, Greenwald and Daniels decided to use photographs, but not video, and only if the person jumping could not be identified. Still, the material can be devastating.

“Even all of us who work here, when I see bits of the exhibition,” Daniels said, pausing for a breath, “it’s very powerful.”

So the architectural design includes “early exits” along the museum route, enabling distressed visitors to duck out without having to pass through the entire exhibition. Disturbing material will be sectioned off with partitions or put in alcoves. Those who want more information can stop at one of several kiosks to gain access to the museum’s archives. Absent from the space so far are any “composites,” the chunks of compressed floors. Many officials and family members say they are the objects that perhaps best capture the destructive force unleashed that day.

“This is something that people 50 years from now should see,” Cassano, the fire chief, said.

Some families are concerned, though, that despite assurances and tests, composites could contain body matter.

“Museum officials thought this was a very interesting exhibit,” said Diane Horning, who lost her 26-year-old son, Matthew. “To us, it was human remains.”

THE FACES OF TERROR

Like a line in a sacred text, a single sentence in the museum’s guidelines generated volumes of conflicting commentary: Exhibits should explore “a factual presentation of what is known of the terrorists, including their methods and means of preparation.”

That sentence was one of the recommendations offered by the Lower Manhattan Development Corp. before it handed off responsibility for the memorial and museum to the foundation in 2006. The two pages of guidelines — composed by the corporation’s 27-member museum advisory committee, after consulting with seven advisers and reviewing 1,070 public comments — were adopted by what is now known as the National September 11 Memorial & Museum at the World Trade Center Foundation as a formal planning document.

The Talmudic-like analysis began immediately. How, for instance, should the museum handle the flood of information about the terrorists’ private lives and plotting that the government’s mammoth investigation was uncovering?

The museum was in a unique position to draw perhaps the most detailed and nuanced portrait of the men, but that was precisely the problem. Officials were wary of being seen as trying to do too much to humanize murderers.

By 2008, Jan Ramirez, the museum’s chief curator, said, “We retreated from that kind of in-depth presentation.”

Only evidence that proved the hijackers’ guilt would be displayed. “There is not a shred of psychoanalysis about what their issues might have been,” Ramirez explained. “You would never want to create a type of interest in their lives that would potentially promote some other zealot.”  Explaining the terrorists’ motivations aroused similar concerns. To some families of victims, asking what caused Sept. 11 “is literally a profane question,” said Rabbi Irwin Kula, president of the National Jewish Center for Learning and Leadership and a participant in the conversation series. “It is like blaming the victim.”

Other families, Greenwald said, “literally took me by the lapel and said, ‘Don’t whitewash this, you’ve got to tell the story.”’

Yet making sense of the attacks is hard to do without delving into the grievances of the attackers. In the end, Daniels said, they reasoned: “al-Qaida was responsible. Therefore we looked at the rise of al-Qaida, and that was in the ’80s.” Thus the museum will begin the tale in 1979 with the Soviet invasion of Afghanistan, where radical Islamic fighters, who gained power with the support of the United States, later gave Osama bin Laden and al-Qaida safe haven.

The tug of war between memorializing and documenting is also encapsulated in the angry debates over the question of displaying the hijackers’ photographs. When the program committee voted on whether to play the cockpit recording of the hijackers’ voices, Daniels reported, everyone there said yes.

The decision on the photographs was more labored. They decided to shrink the images, from 6 by 4 inches to 2 by 1 1/2 inches, the faces a little bigger than a thumbnail. And they will have evidence stickers from the FBI attached. Museum officials, borrowing an idea from the FBI’s in-house Sept. 11 exhibition, placed the photos on a slanted board, in a narrow partitioned alcove.

In that space will be documentation of their activities, including quotations from their final statements, acknowledging their participation. “We’re allowing them to indict themselves as mass murderers, not giving them a platform for propaganda,” Greenwald said.

“Ultimately this is not a museum that is created or designed by committee,” Daniels said. “We’ll listen to everybody, but in the end we have to make the decision.”

After a pause, he added, “There’s almost a comfort level that we’re going to get criticized, no matter what.”

“It’s not always an authoritative museum,” Greenwald later added. “It’s about collective memory.”