More than a year after Hamas’ devastating October 7 attacks on Israel, the country’s military said Thursday it had killed the man it considers to have been the chief architect of that cross-border massacre – raising questions about the future of the war and of the militant group itself, which has faced blow after blow in recent months.

The death of Hamas leader Yahya Sinwar could pose a rare opportunity to strike a ceasefire, US officials say – with Israel having killed several other top Hamas commanders including Ismail Haniyeh, the group’s former political leader, as well as leaders of militant group Hezbollah in Lebanon.

Hamas and Hezbollah are both part of an axis of militant groups backed by Iran.

In a recorded video message Thursday, Israeli Prime Minister Benjamin Netanyahu said Sinwar’s death marked “the beginning of the day after Hamas,” but “the task before us is not yet complete.”

Hamas is yet to comment on the reports of its leader’s death.

Here’s what you need to know.

How did it happen?

Since the October 7 attacks, Israel has poured their resources into a fierce manhunt for Sinwar, declaring him as the most-wanted man in Gaza and a “dead man walking.” At one point, an Israeli military spokesperson said their hunt “will not stop until he is captured, dead or alive.”

And, US officials believe, the Israeli military got close a few times, at one point even obtaining a video that purportedly showed Sinwar with several family members inside a Gaza tunnel – but he continued slipping away. The Israeli military previously surrounded Sinwar’s house and carried out an intensive assault on his hometown of Khan Younis, but could not find him.

That year-long search finally came to an unexpected end on Wednesday in Rafah, southern Gaza. Israeli forces had been in the area during a routine military operation when they came under fire near a building, according to two Israeli sources familiar with the matter.

The troops returned fire with a tank, then flew a drone into the heavily damaged building, according to the Israeli military. The video, shared by the military, shows what seem to be Sinwar’s final moments: he sits alone in a chair, surrounded by dust and rubble, appearing to look directly at the camera. He holds a piece of wood in his hand, and throws it at the drone before the video ends.

It was only then, and when troops inspected the rubble, that they realized Sinwar was among the bodies, according to the Israeli military.

Dental records and other biometrics helped Israel identify the Hamas leader, according to a US official and former official familiar with the matter.

Sinwar had been trying to escape to the north when he was killed, said another Israeli military spokesperson on Thursday. He was found with a gun and more than $10,000 in Israeli shekels, the spokesperson said.

Who was Sinwar?

Sinwar had long been a key player in Hamas, joining the militant group in the late 1980s and quickly rising through the ranks.

He was born in a refugee camp in Gaza, after his family was displaced from the Palestinian village of Al-Majdal – now part of the Israeli city Ashkelon – during the Arab-Israeli war.

As a student, Sinwar became an anti-occupation activist, but he was imprisoned in Israel on several life sentences after being accused of orchestrating murder. He served 23 years before being released as part of a prisoner swap in 2011.

Sinwar returned to Gaza and quickly established his name in Hamas. He founded the group’s feared international intelligence security branch, the Majd, and was known for employing brutal violence against anyone suspected of collaborating with Israel.

He was also viewed as a pragmatic political leader by some: in 2017, Hamas elected Sinwar as the political chief of the Politburo, its main decision-making body in Gaza.

Sinwar was designated a global terrorist by the US Department of State and the European Union in 2015, and was sanctioned by the United Kingdom and France in recent years.

But he rose to greater prominence after the October 7 attacks as one of Israel’s key targets. Israeli officials have called him the “face of evil” and “the butcher from Khan Younis.”

He became one of Hamas’ most senior leaders in August after Ismail Haniyeh was assassinated in Iran. Sinwar had not been seen since the October 7 attacks, likely surviving Israel’s siege of Gaza by bunkering in a vast network of underground tunnels.

What was his role on October 7?

Israel has publicly accused Sinwar of being the “mastermind” behind Hamas’ October 7 attack – though experts say he was likely one of several.

The attack was the deadliest assault on Israel in its history. Hamas and other Palestinian armed groups killed more than 1,200 people, mostly civilians, and took about 250 people into Gaza as hostages.

Sinwar was considered a vital decision-maker and likely the outside world’s main point of contact in Gaza during the intense negotiations over the hostages’ return.

The talks involved senior figures from Israel, Hamas, the United States, Qatar and Egypt.

What comes next?

While it’s too soon to say what may happen next or how Hamas may respond, Sinwar’s killing marks the latest blow to the group – which has seen several top leaders picked off one by one during Israel’s campaign to dismantle Hamas entirely.

Only a day after Haniyeh’s assassination, Israel confirmed it had killed Hamas’ military chief Mohammed Deif during a previous strike – another one of the reported masterminds behind October 7.

With a ceasefire and hostage release deal to pause the war stubbornly stuck for months, senior US officials had clung to the hope that Sinwar might one day be taken out – opening a pathway to a resolution. With him now gone, officials speculate this could be one of the best chances of bringing the Israel-Hamas war to an end, but are reticent to make any predictions about what that will ultimately mean for the volatile region.

US President Joe Biden spoke with Netanyahu on a call Thursday, where “both leaders agreed that there is an opportunity to advance the release of the hostages and that they would work together to achieve this objective,” the prime minister’s office said in a readout.

But much remains unknown – including the fate of Sinwar’s brother.

If Mohammed survived this week, he will likely continue his brother’s hardline negotiating tactics as Israel seeks to extract its remaining hostages from the Palestinian enclave. But until a clear picture emerges, it will be hard to know the militant group’s next move.

And another front of the conflict is ramping up across the Israel-Lebanon border, with Hezbollah announcing a “new and escalating phase” in its war with Israel on Thursday.

Hezbollah, too, has suffered significant losses in recent months – from the deadly pager and walkie-talkie attacks that killed dozens and injured thousands, many of them civilians, to the assassinations of several high-ranking commanders including their chief Hassan Nasrallah last month.

“Sinwar has died, but so many of our people have been killed, and there is no excuse now for Netanyahu to continue the war,” said 22-year-old Mumen Khalili.