The Hamas Chief and the Israeli Who Saved His Life

This is how Dr. Yuval Bitton remembers the morning of Oct. 7. Being jolted awake just after sunrise by the insistent ringing of his phone. The frantic voice of his daughter, who was traveling abroad, asking, “Dad, what’s happened in Israel? Turn on the TV.”

News anchors were still piecing together the reports: Palestinian gunmen penetrating Israel’s vaunted defenses, infiltrating more than 20 towns and military bases, killing approximately 1,200 people and dragging more than 240 men, women and children into Gaza as hostages.

Even in that first moment, Dr. Bitton says, he knew with certainty who had masterminded the attack: Yahya Sinwar, the leader of Hamas in Gaza and Inmate No. 7333335 in the Israeli prison system from 1989 until his release in a prisoner swap in 2011.

But that was not all. Dr. Bitton had a history with Yahya Sinwar.

As he watched the images of terror and death flicker across his screen, he was tormented by a decision he had made nearly two decades before — how, working in a prison infirmary, he had come to the aid of a mysteriously and desperately ill Mr. Sinwar, and how afterward the Hamas leader had told him that “he owed me his life.”

The two men had then formed a relationship of sorts, sworn enemies who nevertheless showed a wary mutual respect. As a dentist and later as a senior intelligence officer for the Israeli prison service, Dr. Bitton had spent hundreds of hours talking with and analyzing Mr. Sinwar, who in the seven months since Oct. 7 has eluded Israel’s forces even as their assault on Gaza has killed tens of thousands and turned much of the enclave to rubble. Now American officials believe Mr. Sinwar is calling the shots for Hamas in negotiations over a deal for a cease-fire and the release of some of the hostages.

Dr. Bitton saw that, in a sense, everything that had passed between himself and Mr. Sinwar was a premonition of the events now coming to pass. He understood the way Mr. Sinwar’s mind worked as well as or better than any Israeli official. He knew from experience that the price the Hamas leader would demand for the hostages might well be one Israel would be unwilling to pay.

And by day’s end, he knew something else: Mr. Sinwar’s operatives had his nephew.

THE DAY HE SAVED Yahya Sinwar’s life, Yuval Bitton was 37, running the dental clinic at the Beersheba prison complex, in the Negev desert of southern Israel. He had taken the job eight years earlier, in 1996, fresh out of medical school, assuming he would be treating guards and other employees.

Instead, he’d ended up with a patient roster of some of Israel’s most hardened prisoners, like the Hamas operatives responsible for suicide attacks at a Jerusalem market and a Passover massacre at the Park Hotel, as well as the ultranationalist Israeli who assassinated Prime Minister Yitzhak Rabin for his peacemaking with the Palestine Liberation Organization. There were times when Dr. Bitton would be drilling the teeth of one terrorist only to learn that outside the prison walls, another had struck.

“During the day you would treat them and at night you come home and cry,” he said. “That happened many, many nights. Once there was a suicide attack near where my parents lived. Sixteen Jews were killed. Who would not cry at night? When you see a small baby being lifted, who wouldn’t cry?”

He tried to compartmentalize. He told himself that as a doctor he was bound by his oath to do no harm. And on particularly bad days, he said, he would remind himself of the words that Israel’s primary architect, David Ben-Gurion, had made his mantra in the years after the nation’s founding: “The State of Israel will be judged not by its wealth, nor by its army, nor by its technology, but by its moral character and human values.”

While some Israeli historians question whether Ben-Gurion always lived by those words, Dr. Bitton took them to heart. It was, he thought, what differentiated him from the prisoners he treated.

PRISON, MR. SINWAR once told an Italian journalist, is a crucible. “Prison builds you,” he said, gives you time to think about what you believe in — “and the price you are willing to pay” for it.

His rite of passage had begun in 1989, two years after the first intifada erupted, protesting Israel’s occupation of the West Bank and Gaza Strip. He was 27, with a reputation for extreme brutality, convicted of murdering four Palestinians whom Hamas suspected of collaborating with Israel.

He was born in a refugee camp in southern Gaza, where his parents had been forced to live after what Palestinians call the Nakba, or catastrophe, when they were displaced from their homes during the wars surrounding the founding of the State of Israel in 1948. In conversations with fellow prisoners, Mr. Sinwar spoke of how his refugee childhood had led him to Hamas.

“Something he always remembered is that all the men in the camp would go to one bathroom, and the women to another,” said Esmat Mansour, a fellow prisoner held from 1993 to 2013 for killing an Israeli settler. “There was a daily line and you had to wait. And how they distributed food and the humiliation they would undergo. It isn’t something special to him, but it apparently impacted him a lot.”

Mr. Sinwar had been recruited by Hamas’s founder, Sheik Ahmed Yassin, who made him chief of an internal security unit known as Al Majd. His job was to find and punish those suspected of violating Islamic morality laws or cooperating with the Israeli occupiers.

In an interrogation after his arrest in 1988, he dispassionately described shooting one man, strangling another with his bare hands, suffocating a third with a kaffiyeh, and choking and punching a fourth before tossing him in a hastily dug grave. Records of the interrogation make clear that, far from being remorseful, Mr. Sinwar saw beating confessions out of the collaborators as a righteous duty. One of them, he told interrogators, had even said that “he realized he deserved to die.”

Mr. Sinwar continued his campaign against informants from behind bars. Israeli authorities believed he had ordered the beheadings of at least two prisoners he suspected of snitching. Hamas operatives would throw their severed body parts out of the cell doors and tell the guards to “take the dog’s head,” Dr. Bitton said.

But if Mr. Sinwar was feared by his fellow inmates, he was also respected for his resourcefulness. He tried to escape several times, once surreptitiously digging a hole in his cell floor in hopes of tunneling under the prison and exiting through the visitor center. And he found ways to plot against Israel with Hamas leaders on the outside, managing the smuggling of cellphones into the prison and using lawyers and visitors to ferry messages out.

Often, the message was about finding ways to kidnap Israeli soldiers to trade for Palestinian prisoners. Years later, Mr. Sinwar would say that “for the prisoner, capturing an Israeli soldier is the best news in the universe, because he knows that a glimmer of hope has been opened for him.”

“They were formative years,” Ghazi Hamad, a senior Hamas official who serves as an informal spokesman, said in an interview. “He developed a leadership personality in every sense of the word.”

He also became fluent in Hebrew, taking advantage of an online university program, and devoured Israeli news, to better understand his enemy. A routine search of his cell yielded tens of thousands of pages of painstakingly handwritten Arabic — Mr. Sinwar’s translations of contraband Hebrew-language autobiographies written by the former heads of Israel’s domestic security agency, Shin Bet. According to Dr. Bitton, Mr. Sinwar surreptitiously shared the translated pages so other inmates could study the agency’s counterterrorism tactics. He liked to call himself a “specialist in the Jewish people’s history.”

“They wanted prison to be a grave for us, a mill to grind our will, determination and bodies,” Mr. Sinwar once told supporters. “But, thank God, with our belief in our cause we turned the prison into sanctuaries of worship and academies for study.”

Hamas, an offshoot of the Muslim Brotherhood, elects its leaders democratically, and that structure was mirrored behind bars. In each prison, one committee was charged with making quotidian decisions — who slept in the top bunk, what to watch during allotted TV hours — while another meted out punishments to suspected collaborators, and still others oversaw things like divvying up money sent by Hamas leaders that could be used to purchase food at the commissary.

An elected “emir,” along with members of a high council called the “haya,” ruled over this structure for limited terms. For much of Mr. Sinwar’s time in prison, he alternated as emir with Rawhi Mushtaha, a confidant who had been convicted alongside him for killing collaborators. It was Mr. Sinwar’s turn in 2004.

AT THE TIME, the episode seemed of little consequence. After all, Dr. Bitton said, Mr. Sinwar was supposed to be serving four life terms.

As a dentist in Israel, Dr. Bitton had also trained in general medicine, and was often called upon to assist the three other prison doctors, stitching up wounds or helping with a tricky diagnosis. So when he emerged from seeing his dental patients that day in early 2004 to find several clearly perplexed colleagues surrounding a disoriented Mr. Sinwar, Dr. Bitton did what a doctor does. He joined them.

“What’s going on?” he asked the prisoner.

The two men had met on a number of occasions. Dr. Bitton often wandered back to the prisoners’ wings, partly out of curiosity about how some of Israel’s most fervent enemies thought, and partly because the trust he engendered as a doctor made him a useful intermediary when prison administrators wanted to know what was going on. Just as Mr. Sinwar had learned Hebrew, Dr. Bitton had taught himself Arabic. He became such a regular presence in the cellblocks that some prisoners suspected, wrongly, that he might be an intelligence plant.

Israeli and Palestinian watchdog groups have periodically published scathing reports on conditions for Palestinian prisoners — overcrowded cells lacking proper sanitation and ventilation, harsh interrogations and, in some cases, years of solitary confinement and withholding of proper medical care.

Against that backdrop, Mr. Mansour said, Dr. Bitton stood out. “He treated us like humans.”

“He bought the hearts of the prisoners, truly. He would go into their cells, drink with them and eat with them,” he said. “If there was a problem, he would call and help.”

Lately Dr. Bitton had been working to persuade Mr. Sinwar and others to cooperate with Israeli researchers studying suicide bombings. But in the examining room, Mr. Sinwar didn’t seem to know him.

“Who are you?” Dr. Bitton recalled him asking.

“It’s me, Yuval.”

“Wow, I’m sorry — I didn’t recognize you,” Dr. Bitton said the prisoner replied, before describing his symptoms.

He would stand for prayer and then fall. As he spoke, he seemed to drift in and out of consciousness. But for Dr. Bitton, the most telling sign was Mr. Sinwar’s complaint of a pain in the back of his neck. Something is wrong with his brain, the dentist told his colleagues, perhaps a stroke or an abscess. He needed to go to the hospital, urgently.

He was rushed to the nearby Soroka Medical Center, where doctors performed emergency surgery to remove a malignant and aggressive brain tumor, fatal if left untreated. “If he had not been operated on, it would have burst,” Dr. Bitton said.

A few days later, Dr. Bitton visited Mr. Sinwar in the hospital, together with a prison officer sent to check the security arrangements. They found the prisoner in bed, hooked up to monitors and an IV, but awake. Mr. Sinwar asked the officer, who was Muslim, to thank the dentist.

“Sinwar asked him to explain to me what it means in Islam that I saved his life,” Dr. Bitton recalled. “It was important to him that I understood from a Muslim how important this was in Islam — that he owed me his life.”

MR. SINWAR RARELY if ever spoke to the Israeli prison authorities. But now he began meeting regularly with the dentist, to drink tea and talk.

They would meet back in the cellblocks, two men with strikingly similar features — cropped, prematurely graying hair; dark, quizzically arched eyebrows; high cheekbones. Dr. Bitton, a loquacious, easygoing man, often joshed with the other prisoners, getting them to open up about their families or sports. But with Mr. Sinwar, the talk was all business and dogma.

“The conversations with Sinwar were not personal or emotional,” he said. “They were only about Hamas.”

Mr. Sinwar knew the Quran by heart, and he coolly laid out his organization’s governing doctrines.

“Hamas sees the land we live on as the holy land, like, ‘This is ours, you don’t have a right to live in this land,’” Dr. Bitton said. “It wasn’t political, it was religious.”

Was there no chance, then, for a two-state solution? Dr. Bitton would press him.

Never, Mr. Sinwar would say. Why not? Dr. Bitton would respond.

Because this is the land of Muslims, not for you — I can’t sign away this land.

In a search of his cell, guards had confiscated a handwritten novel that Mr. Sinwar finished at the end of 2004, after the surgery. “You couldn’t make a Hollywood movie about it,” Dr. Bitton laughed. “But it was about the relationship between men, women and the family in Islam.” At least one copy was smuggled out; The New York Times found a typed PDF in an online library.

The novel, “The Thorn and the Carnation,” is a coming-of-age story that limns Mr. Sinwar’s own life: The narrator, a devout Gazan boy named Ahmed, emerges from hiding during the 1967 Arab-Israeli war to a life under Israeli occupation. In their cruelty, the occupiers cause the “chests of youth to boil like a cauldron.” In retaliation, Ahmed’s friends and family attack them with knives, ambush them with Molotov cocktails and hunt collaborators so as to “gouge out the eyes that the occupier sees us with from the inside.”

Woven throughout is the theme of the unending sacrifice demanded by the resistance. At university, where he is recruited to Hamas, Ahmed becomes infatuated with a woman he sees walking to and from class. “I am not exaggerating when I say that she truly surpasses the full moon,” he says. Yet their relationship, chaste and proper according to Muslim values, never develops; the reader never even learns the woman’s name.

“I decided to end my love story, if it can even be called a love story,” the narrator says. “I realized that ours is the bitter story of Palestine, for which there is only room for one love … one passion.”

But if Mr. Sinwar, unmarried at the time, ever entertained the notion of an alternative path for himself, he did not share his thoughts with Dr. Bitton. (Indeed, even after his release from prison and subsequent marriage, he has said very little publicly on the subject of his own family, except to note that “the first words my son spoke were ‘father,’ ‘mother’ and ‘drone.’”)

At Beersheba, Mr. Sinwar was unquestionably a prison chieftain, Dr. Bitton said, but he didn’t put on airs — a humble ascetic who shared cooking duties and other chores with more junior inmates.

Every week or so, he would make an improvised knafeh, a Palestinian dessert of sweet cheese and shredded pastry drenched in syrup. The prisoners always awaited his knafeh, Dr. Bitton said. They really liked it — and so did Dr. Bitton, who understood the breaking of bread together as a way to cultivate the relationship.

“I tried it,” he allowed. “Listen, they know how to make knafeh.”

Dr. Bitton was under no illusion about whom he was dealing with. A prison assessment that Dr. Bitton said he helped compile called Mr. Sinwar cruel, cunning and manipulative, an authoritative man with “the ability to carry crowds” who “keeps secrets even inside prison amongst other prisoners.”

Still, there was a certain transactional honesty to their conversations. Each man knew the other had an agenda.

Just as Dr. Bitton probed to better understand the schisms between Hamas and the other Palestinian factions inside the prison, Mr. Sinwar returned again and again to the fissures in Israeli society that he read about in the Hebrew news media, between rich and poor and Sephardic and Ashkenazi and secular and orthodox Jews.

“Now you’re strong, you have 200 atomic warheads,” Mr. Sinwar would say. “But we’ll see, maybe in another 10 to 20 years you’ll weaken, and I’ll attack.”

In 2006, after Israel’s withdrawal from Gaza, Hamas stunned political observers by winning the largest number of seats in the Palestinian Authority’s legislative elections.

Israeli authorities, worried that the election would help legitimize a group that the United States and European Union had designated a terrorist organization, devised a plan to remind the world of Hamas’s true colors by giving some of its incarcerated leaders a media platform on “60 Minutes” and in an interview with Israeli television. Dr. Bitton was tasked with selling the idea to Mr. Sinwar, who would have to sign off.

“Speak freely, you can say whatever you want about Israel,” Dr. Bitton told Mr. Sinwar and other prisoners.

The plan worked, from Dr. Bitton’s perspective. When Abdullah Barghouti, who had organized suicide bombings that killed 66 people, was asked on “60 Minutes” whether he regretted his deeds, he readily answered yes. “I feel bad, ’cause the number only 66,” he said.

Mr. Sinwar, for his part, tried to use his first and only interview with an Israeli television outlet to send a savvier message. With Dr. Bitton looking on, he told the interviewer that Israelis should “be scared” about Hamas’s election victory. But, he added in comments that weren’t aired, much depended on what the Israeli government did next. “From our perspective, we have a right that we’re asking from the Israeli leadership,” he said. “We aren’t asking for the town.”

The next year, to great alarm in Israel, Hamas wrested full control over Gaza in a violent power struggle with Fatah, a secular rival political party.

This was the time, Dr. Bitton decided, to channel the relationships he had built with Mr. Sinwar and other imprisoned Palestinian leaders into a new role, one that would not leave him feeling so conflicted. He applied to become an officer in the Prison Intelligence Service, and after a short course was assigned to Ketziot prison in 2008. The man who “doesn’t understand the motives and roots of their enemy,” he explained, “will not be able to prevent those organizations from doing what they want.”

DR. BITTON WAS quickly thrown into a monumental challenge. Two years earlier, in 2006, an Israeli soldier, Gilad Shalit, had been kidnapped in a daring cross-border raid. Among his captors was none other than Mr. Sinwar’s brother.

The kidnapping profoundly shook Israeli society, with its credo that not a single soldier should be left behind. As the Israeli government, working through a back channel with a team of international intermediaries, attempted to negotiate a prisoner swap, Dr. Bitton was tasked with using his connections to imprisoned Hamas leaders to glean intelligence on what they would accept.

By 2009, Israel had agreed in principle to exchange 1,000 Palestinian prisoners for Mr. Shalit. Mr. Sinwar “was managing the negotiations from inside the prison with a group of brothers who were also with him,” according to Ghazi Hamad, the informal Hamas spokesman, who was involved in the negotiations.

There was only one problem: Despite being on the list himself, Mr. Sinwar didn’t think the deal was good enough, according to Gerhard Conrad, a retired German intelligence officer involved in brokering the Shalit deal.

Mr. Sinwar was insisting on freeing “the so-called impossibles,” Mr. Conrad said. Those were the men serving multiple life sentences, men like Mr. Barghouti and Abbas al-Sayed, who had masterminded the Passover suicide attack that had killed 30 people at the Park Hotel.

Saleh al-Arouri, a founder of Hamas’s armed wing, the Qassam Brigades, and a leader of prisoners from the West Bank, approached Dr. Bitton. Would he help push against Mr. Sinwar’s obstinacy?

Mr. al-Arouri “understood they had to compromise — that we would not release everyone,” Dr. Bitton said. “He was more pragmatic.”

Recognizing that the rift between Mr. Sinwar and Mr. al-Arouri could potentially be used to advance the Shalit negotiations, Dr. Bitton got his bosses to sign off on a plan aimed at deepening the division. At Mr. al-Arouri’s request, prison officials brought together 42 influential West Bank inmates from three separate prisons so that Mr. al-Arouri could win them to his side.

But pressuring Mr. Sinwar turned out to be much harder.

Dr. Bitton saw what he was up against in 2010, when, amid the stalled Shalit negotiations, Mr. Sinwar tried to compel all 1,600 Hamas prisoners to join a hunger strike that would have left many of them dead. The goal wasn’t even to free prisoners, just to release two from long-term solitary confinement. In that moment, Dr. Bitton said, he realized there would never be a Shalit deal as long as Mr. Sinwar remained in the way.

“He was willing to pay a heavy price for principle,” Dr. Bitton said, “even if the price wasn’t proportional to the goal.”

Even after the Shalit negotiators managed to convince the Israelis in 2011 to release additional prisoners, bringing the total to 1,027 — including some, though not nearly all of the “impossibles” — Mr. Sinwar remained opposed.

But by this point, Mr. al-Arouri had been released from prison and was a member of the Hamas negotiating team, led by Ahmad al-Jabari, a top commander who had led the raid that captured Mr. Shalit. Under pressure from Egyptian mediators, the team concluded that this was as good a deal as they were going to get.

Mr. Sinwar’s authority had been diluted. But just to be sure, the Israelis put him in solitary confinement until the deal was done. (Mr. al-Arouri was killed in an Israeli airstrike this past January.)

On Oct. 18, 2011, Dr. Bitton stood in the yard of Ketziot prison, watching as Mr. Sinwar boarded a bus to Gaza. Having witnessed the persuasive power of Mr. Sinwar’s leadership up close, Dr. Bitton said he had urged the negotiators not to free him. But he was overruled, he said, because Mr. Sinwar “didn’t have as much Jewish blood on his hands” as some of the others.

“I thought you need to look at the capabilities of the prisoner to use their abilities against Israel and not just what he did — his potential,” Dr. Bitton said.

In news video footage from that day, Mr. Sinwar does not look all that pleased either, scowling on a makeshift stage in central Gaza City as Ismail Haniyeh, then leader of Hamas in Gaza, gleefully waves to the thousands gathered to celebrate the prisoners’ release. Hours later, in an interview with Hamas’s al-Aqsa TV, a defiant Mr. Sinwar made a promise.

“We shall spare no efforts to liberate the rest of our brothers and sisters,” he said. “We urge the Qassam Brigades to kidnap more soldiers to exchange them for the freedom of our loved ones who are still behind bars.”

“He told us what he was going to do,” Dr. Bitton said. “We didn’t want to listen.”

ABOUT 6:30 A.M. on Oct. 7, Dr. Bitton’s nephew, Tamir Adar, woke up in Nir Oz, a kibbutz less than two miles from the Gaza border. Mr. Adar, 38, worked as a farmer, and he normally rose early so that he would have time to enjoy the long summer afternoons, drinking beer as he watched his daughter and son splash around in the community pool.

That morning, as air raid sirens blared, rockets pierced the sky and sporadic gunfire ricocheted off walls, Mr. Adar left his wife and children in their house’s small safe room and went out to join the kibbutz’s armed emergency response team.

At 8:30 a.m., he sent his wife a WhatsApp message: She should not open the safe-room door, not even if he came pleading to be let in. The kibbutz had been overrun.

At 4 p.m., soldiers finally arrived and called residents out of their safe rooms. Mr. Adar was nowhere to be found. His mother, Yael, called her brother, Dr. Bitton: “Tamir has disappeared.”

Roughly 100 Nir Oz residents — a quarter of the population — had been killed or kidnapped in the Hamas raid. The world quickly knew that Mr. Adar’s paternal grandmother, 85-year-old Yaffa Adar, was among them, as viral video showed armed militants carrying her to Gaza in a stolen golf cart. It would be three weeks before Israeli officials could confirm that Mr. Adar had been taken hostage, too.

Before, his mother worked as the administrator for a school district near the Gaza border. Now she gave herself over to the hostages’ cause, attending marches and demonstrations to pressure the government into striking a deal with Hamas for their release.

“One day you’re hopeful and the next in despair,” she said. “One day you’re crying and the next you’re able to gather yourself.”

She wondered whether she should ask her brother to leverage his connections, but decided against it. “What could I tell him?” she said. “Call Sinwar?”

In the years since the Shalit deal, Dr. Bitton had climbed the ranks of the Israeli Prison Service, becoming the head of its intelligence division and then a deputy commander overseeing 12 prisons before retiring in 2021. Mr. Sinwar had traced a parallel arc. After his release, he was elected to a role akin to Hamas defense minister. And in 2017, he was elected leader of Hamas in Gaza, overseeing all aspects of life on the Strip.

It hadn’t escaped Dr. Bitton’s notice that the Hamas assault came at a time of deep division in Israel, the nation wracked by protests over Prime Minister Benjamin Netanyahu’s efforts, demanded by the right-wing parties crucial to his political survival, to dilute the power of Israel’s Supreme Court. It was precisely the type of schism that Mr. Sinwar had spoken of years before at Beersheba, when he said he would attack at a time of internal strife.

Dr. Bitton held small hope for his nephew’s release. For Mr. Sinwar, the hostages were a means to an end — freeing the Palestinian prisoners left behind in the Shalit deal and putting the Palestinian cause back on the world stage. Even if Mr. Sinwar knew who his nephew was, Dr. Bitton said, “at the end he looks at us as Jews.”

Still, in one of their last conversations, on the day Mr. Sinwar was freed, the Hamas leader had again thanked him for saving his life. Mr. Sinwar had even asked for his phone number, though Dr. Bitton had to refuse because prison employees are forbidden to communicate with Hamas leaders on the outside. He believed that Mr. Sinwar would feel bound by a kind of code, and that if he was made aware that Hamas held Dr. Bitton’s nephew, he at least would not allow him to be mistreated.

“Beyond the fact that we are enemies, at the end of the day there is also his personal outlook,” Dr. Bitton said. “In my opinion, he would treat him the same way I did, saving his life despite being an enemy.”

Several weeks after the Hamas attack, in the hope that Mr. Sinwar was still an avid follower of Israeli news media, Dr. Bitton decided to give a television interview. In it, he said only that he had been part of a team that had diagnosed Mr. Sinwar decades before, and that his nephew was among the hostages. (In other interviews, he similarly downplayed his role, because, he said, he was worried about how he might be perceived by a nation in mourning.)

In late November, Mr. Adar’s grandmother was released in a weeklong cease-fire deal that saw 105 of the hostages freed, mostly women and children. What Dr. Bitton knew but could not say in his family’s moment of joy was that Mr. Sinwar would hold on to military-age men like Mr. Adar until the very end, to guarantee his own survival.

“Can I tell my sister that they’re releasing Yaffa Adar, Tamir’s grandma, and that that will be the last release and Tamir will remain there? I can’t say it, but I know him and I know what he’ll do,” Dr. Bitton said. “That’s why I stayed silent, but I’m eating my heart out.”

Yet there was reason to believe that his nephew was still alive. In the wake of Dr. Bitton’s TV interview, Israeli intelligence learned that Mr. Sinwar was asking about Mr. Adar’s well-being, and that subordinates had assured him that he was all right.

It turned out the subordinates had asked after the wrong person. On Jan. 5, the government told the family what new intelligence showed: Wounded while defending his kibbutz, Mr. Adar had apparently died not long after being dragged into Gaza, one of at least 35 hostages believed to be dead, among roughly 125 still being held.

Dr. Bitton returned to Nir Oz on a sunny winter morning. Blackened buildings peeked out between columnar cactuses, deafening booms from artillery shells interrupted chirping parrots and cooing doves, and an acrid smell still hung in the air. “The smell of death,” Dr. Bitton said, wrinkling his nose.

Rounding a corner, he stopped. “That’s his blood,” he said, his face tightening in grief as he pointed toward a concrete wall that once hid the kibbutz’s dumpsters, now a dark-stained marker of his nephew’s last stand. And nearby, a small memorial, a fleet of toy tractors.

“Do you see what’s lost?” Dr. Bitton said. “It’s like that here. No one remains, just birds and stories.”

These days, Dr. Bitton meets regularly with the hostages’ families, sharing everything he learned about Mr. Sinwar, to help them manage expectations. In recent weeks, international negotiators have pressed Israel and Hamas to accept a deal that, in its first phase, would see some of the hostages exchanged for many more Palestinian prisoners and a temporary cease-fire, according to officials familiar with the process. But Hamas has held out for a total cessation of hostilities that would leave it in charge of Gaza, a red line for the Israeli government.

“I tell the families not to get their hopes up,” Dr. Bitton said. “In this situation there is no chance.”

Dr. Bitton and his sister have revisited, over and again, that long-ago day in the prison infirmary. Ms. Adar said they try to laugh at the “absurdity” of it all. “On the one hand my brother saved a life, and on the other his sister lost her boy to the same person he saved.”

She assures him there was nothing else he could have done.

“These are our values. Yuval never would have acted differently, never, and neither would I,” she said. “But in the end we were screwed.”

First and foremost by their own government, they said. Hamas is Hamas, as Dr. Bitton put it. “With Sinwar, I know he wants to destroy us,” Ms. Adar echoed. “My greatest anger is that there was no one to defend our borders.”

Not everyone in Israel seems to see it that way. Sitting together in a cafe in Eilat, a town on the Red Sea where the survivors of Nir Oz were first relocated, brother and sister were approached by a stranger. The woman fixed her gaze on Dr. Bitton, apparently recognizing him from his interview on TV. She had a question.

“Why did you save him?” she asked. “Why?”

Hwaida Saad contributed reporting from Beirut, Lebanon. Julie Tate contributed research.