In January, Israeli and American officials thought they had caught a break in the hunt for one of the world’s most wanted men.
Israeli commandos raided an elaborate tunnel complex in the southern Gaza Strip on Jan. 31 based on intelligence that Yahya Sinwar, the Hamas leader, was hiding there, according to American and Israeli officials.
He had been, it turned out. But Mr. Sinwar had left the bunker beneath the city of Khan Younis just days earlier, leaving behind documents and stacks of Israeli shekels totaling about $1 million. The hunt went on, with a dearth of hard evidence on his whereabouts.
Since the deadly Oct. 7 attacks in Israel that he planned and directed, Mr. Sinwar has been something of a ghost: never appearing in public, rarely releasing messages for his followers and giving up few clues about where he might be.
He is by far Hamas’s most important figure, and his success in evading capture or death has denied Israel the ability to make a foundational claim: that it has won the war and eradicated Hamas in a conflict that has decimated the group’s ranks but also destroyed the Gaza Strip and killed tens of thousands of civilians.
American and Israeli officials said Mr. Sinwar abandoned electronic communications long ago, and he has so far avoided a sophisticated intelligence dragnet. He is believed to stay in touch with the organization he leads through a network of human couriers. How that system works remains a mystery.
It is a playbook used by Hamas leaders in the past, and by other terrorist leaders like Osama bin Laden. And yet Mr. Sinwar’s situation is more complex, and even more frustrating to American and Israeli officials.
Unlike bin Laden in his last years, Mr. Sinwar is actively managing a military campaign. Diplomats involved in cease-fire negotiations in Doha, Qatar, say that Hamas representatives insist they need Mr. Sinwar’s input before they make major decisions in the talks. As the most respected Hamas leader, he is the only person who can ensure that whatever is decided in Doha is implemented in Gaza.
Interviews with more than two dozen officials in Israel and the United States reveal that both countries have poured vast resources into trying to find Mr. Sinwar.
Officials have set up a special unit inside the headquarters of Shin Bet, Israel’s domestic intelligence service, and American spy agencies have been tasked with intercepting Mr. Sinwar’s communications. The United States has also provided ground-penetrating radar to Israel to help in the hunt for him and other Hamas commanders.
Killing or capturing Mr. Sinwar would undoubtedly have a dramatic impact on the war. American officials believe it would offer Prime Minister Benjamin Netanyahu of Israel a way to claim a significant military victory and potentially make him more willing to end military operations in Gaza.
But it is less clear what effect Mr. Sinwar’s death would have on negotiations for the release of hostages seized on Oct. 7. Removing him might make his successors far less willing to make a deal with Israel.
Communicating with Mr. Sinwar has become more difficult, said Israeli, Qatari, Egyptian and American officials. He used to respond to messages within days, but the officials said that it has taken much longer to get a response from him in recent months, and that some of his deputies at times have been his proxies in those discussions.
Mr. Sinwar, who is 61, was declared the group’s top political leader in early August, days after Ismail Haniyeh, the previous political chief, was killed in an Israeli assassination plot in Tehran.
But, in reality, Mr. Sinwar has long been considered Hamas’s de facto leader, even if the group’s political operatives based in Doha held the official leadership titles.
The pressure on the Hamas leader has made it far more difficult for him to communicate with military commanders and direct day-to-day operations, although American officials said that he still has the ability to dictate the group’s broad strategy.
It was weeks after the Oct. 7 attacks, which killed at least 1,200 people, when a special committee of senior Israeli intelligence and military officials approved a kill list of top Hamas commanders and political officials. Many of the men on the list, including Mr. Haniyeh, have been killed in the months since.
With each assassination, the Israeli defense minister, Yoav Gallant, has put an “X” over a name on the diagram of the Hamas leadership he keeps on his wall.
But Mr. Sinwar, the most important of all, remains at large.
Life Underground
Before the war, Mr. Sinwar was a towering presence in Gaza.
He gave interviews, presided over military exercises and even made a televised appearance to present an award to a show depicting a Hamas attack on Israel — an eerie precursor to Oct. 7.
During the first weeks of the war, Israeli intelligence and military officials believe that Mr. Sinwar was living in a warren of tunnels beneath Gaza City, the largest city in the strip and one of the first targeted by Israeli military forces.
During one early raid on a tunnel in Gaza City, Israeli soldiers found a video — filmed days earlier — of Mr. Sinwar in the midst of moving his family to a different hiding spot under the city. Israeli intelligence officials believe that Mr. Sinwar kept his family with him for at least the first six months of the war.
Back then, Mr. Sinwar still used cellular and satellite phones — made possible by cell networks in the tunnels — and from time to time spoke to Hamas officials in Doha. American and Israeli spy agencies were able to monitor some of those calls but were not able to pinpoint his location.
As Gaza ran low on fuel, Mr. Gallant pushed for new shipments to Gaza to power generators needed to keep the cell networks running so that the Israeli eavesdropping could continue — over the objections of ultra right members of the Israeli government who wanted the fuel shipments cut off to punish the residents of Gaza.
During this period, the spy agencies gained glimpses of his life underground, including his voracious consumption of Israeli news media and his insistence on watching the 8 p.m. news on Israeli TV.
In November, a freed Israeli hostage described how Mr. Sinwar had addressed a large number of Israeli captives not long after the Oct. 7 attacks. Speaking in Hebrew, which he learned during his years in an Israeli prison, Mr. Sinwar told them that they were safe where they were, and that no harm would come to them, according to the hostage’s account.
Israeli officials said that all Hamas operatives hiding underground, even Mr. Sinwar, must occasionally come out of the tunnels for health reasons. But the tunnel network is so vast and complex — and Hamas fighters have such good intelligence about the whereabouts of Israeli troops — that Mr. Sinwar can sometimes come above ground without being discovered.
Mr. Sinwar eventually moved south to Khan Younis, the city where he was born, Israeli and American officials believe, and probably occasionally traveled from there to the city of Rafah through a stretch of tunnel.
By the time the Khan Younis bunker was raided on Jan. 31, Mr. Sinwar had fled, Israeli officials said.
He stayed one step ahead of his pursuers, who sometimes made boastful comments about how close they were to finding him. In late December, as Israeli military units began excavating tunnels in one area of the city, Mr. Gallant bragged to reporters that Mr. Sinwar “hears the bulldozers of the I.D.F. above him, and he will meet the barrels of our guns soon.”
It appears Mr. Sinwar fled the Khan Younis bunker in some haste, leaving the many piles of Israeli shekels behind.
Shared Interests
Almost immediately after the Oct. 7 attacks, Israeli military intelligence and Shin Bet, Israel’s domestic security service, established a cell inside Shin Bet headquarters with the singular mission of finding Mr. Sinwar.
The C.I.A. also set up a task force, and the Pentagon dispatched special operations troops to Israel to advise the Israel Defense Forces on the looming war in Gaza.
The United States, which considers Hamas a terrorist organization, and Israel established channels to share information about the location of Mr. Sinwar and other top Hamas commanders, and the hostages.
“We’ve devoted considerable effort and resources to the Israelis for the hunt for the top leadership, particularly Sinwar,” said Jake Sullivan, the White House national security adviser. “We’ve had people in Israel sitting in the room with the Israelis working this problem set. And obviously we have a lot of experience hunting high-value targets.”
In particular, the Americans have deployed ground-penetrating radar to help map the hundreds of miles of tunnels they believe are under Gaza, with new imagery combined with Israeli intelligence gathered from captured Hamas fighters and troves of documents to build out a more complete picture of the tunnel network.
One senior Israeli official said American intelligence support had been “priceless.”
The Israelis and Americans have a mutual interest in locating Hamas commanders and the dozens of hostages, including Americans, who remain in Gaza.
But one person familiar with the intelligence-sharing arrangement, who discussed it on the condition of anonymity, describes it as often “very lopsided” — with the Americans sharing more than the Israelis give in return. At times, the person said, the Americans provide information about Hamas leaders in the hopes that the Israelis will direct some of their own intelligence resources toward finding the American hostages.
Rise to the Top
During the 1980s, in the years after he was recruited by Hamas’s founder, Sheik Ahmed Yassin, Mr. Sinwar’s influence in the group grew steadily.
He took over as the head of Hamas’s internal security unit, a group charged with finding and punishing Palestinians suspected of collaborating with Israeli authorities as well as anyone who commits blasphemy.
He spent years in an Israeli prison but was released in October 2011 along with more than 1,000 other prisoners as part of an exchange for Gilad Shalit, an Israeli soldier captured by Hamas.
In 2017, Mr. Sinwar was named Hamas’s leader in Gaza.
While he has had an outsized impact on decision-making within Hamas, Mr. Sinwar has shaped his positions in close coordination with a group of Hamas political and military leaders in Gaza, according to analysts who have studied Hamas.
The circle of confidants has included Marwan Issa, a Hamas military commander killed in March; Rawhi Mushtaha, a member of Hamas’s political office in Gaza; Izzeldin al-Haddad, a senior commander in the military wing; Mohammed Sinwar, Mr. Sinwar’s brother and a top official in the military wing; and Muhammad Deif, the leader of the military wing, according to Ibrahim al-Madhoun, an Istanbul-based expert who maintains a close relationship with Hamas.
But Mr. Sinwar’s network of advisers has been steadily shrinking: Some top Hamas commanders have been killed, some captured, and others were outside of Gaza when the war began and have not been able to return since.
Mr. Deif was the most senior adviser to Mr. Sinwar, but was less disciplined than his boss. He came above ground far more regularly, allowing Western intelligence agencies to pinpoint his whereabouts.
It was on one of those occasions, Israeli officials say, when he was killed in an airstrike.
Adam Rasgon in Jerusalem contributed reporting.