Israel says it is investigating the possibility that Hamas leader Yahya Sinwar, a mastermind of the October 7, 2023, attack that sparked the war in Gaza, was killed during a military operation. Authorities conducted DNA tests on a body to determine if it was him, an Israeli security official said.

The army said in a statement that three militants were killed during operations in Gaza, without specifying where or elaborating.

There was no immediate comment from Hamas on the report.

Sinwar’s death would mark a key moment in Israel’s years-long offensive against the militant group and could complicate efforts to free dozens of hostages held in Gaza.

Sinwar became head of Hamas after the killing of its previous leader, Ismail Haniyeh, in an explosion in Iran in July, which was widely blamed on Israel.

Some things you should know about Sinwar:

From refugee camp to Hamas militant

Sinwar was born in 1962 in a refugee camp in the Gaza city of Khan Younis. He was one of the first members of Hamas, which was founded in 1987. He eventually headed the group’s security wing, which was involved in purging informants for Israel.

Israel arrested him in the late 1980s and he admitted to killing twelve suspected collaborators, a role that earned him the nickname “The Butcher of Khan Younis.” He was sentenced to four life sentences for crimes including the murder of two Israeli soldiers.

A prison leader

Sinwar organized strikes in the prison to improve working conditions. He also studied Hebrew and Israeli society.

He survived brain cancer in 2008 after being treated by Israeli doctors.

Sinwar was one of more than a thousand Palestinian prisoners released by Prime Minister Benjamin Netanyahu in 2011 as part of a trade for an Israeli soldier captured by Hamas in a cross-border raid.

Ascend to Gaza power

When Sinwar returned to Gaza, he quickly rose through the Hamas leadership ranks with a reputation for ruthlessness. He is widely believed to have been behind the 2016 killing of another top Hamas commander, Mahmoud Ishtewi, in an internal power struggle.

Sinwar became head of Hamas in Gaza, effectively gaining control of the area, and worked with Haniyeh to align the group with Iran and its allies in the region, while also building up the group’s military capabilities .

The October attack on Israel

Sinwar, along with Mohammed Deif, the head of Hamas’s armed wing, is believed to have engineered the surprise October 7 attack on Israel.

The attack killed about 1,200 people, mostly civilians, and sparked a war that health authorities there say has killed more than 42,000 Palestinians in Gaza.

Hamas said it launched the attack in retaliation for Israel’s treatment of Palestinians and to put the Palestinian cause back on the world agenda.

The International Criminal Court prosecutor applied for arrest warrants for Sinwar, Deif and Haniyeh in May for their alleged role in the attack.

Israel said it killed Deif in an attack in July, while Hamas says he is still alive.

Where would this leave Hamas?

Sinwar has been in hiding since the attack and ceasefire negotiators have said it could take several days for messages to be sent and received from him.

Even before he became Hamas’ top leader, Sinwar was believed to have the final say on a deal to release hostages held by the militant group. There are about 100 hostages remaining in Gaza, about a third of whom are believed to be dead.

It is unclear who would replace Sinwar, and what that could mean for ceasefire efforts, which stalled in August after months of negotiations between the United States, Egypt and Qatar.

Hamas has hundreds of thousands of supporters in Gaza, the Israeli-occupied West Bank and Palestinian refugee camps across the region. Some of the top leaders are based in Qatar, which has served as a mediator between Israel and the militant group.

Israel has arrested and killed several top Hamas leaders and militant commanders over the years, and the militant group quickly replaced them. But it has never waged a prolonged war against Israel, which says it has killed dozens of high-ranking militants and more than 17,000 fighters, although it has provided no evidence for the latter figure.

Other updates from the Israel-Hamas were

Israeli forces continue a week-plus major air and ground assault on the Jabaliya refugee camp in northern Gaza. On Thursday, an Israeli attack hit a school housing displaced Palestinians, killing at least 28 people, according to the Gaza Health Ministry.

Fares Abu Hamza, head of the Health Ministry’s emergency unit in northern Gaza, said the dead included a woman and four children, correcting an earlier report of five children. He said dozens of people were injured.

The Israeli military said it targeted a Hamas and Islamic Jihad command center at the school. It included a list of about a dozen names of people it identified as militants who were present when the strike was called. It was not immediately possible to verify the names.

Israel has repeatedly hit tent camps and schools housing displaced people in Gaza. The Israeli army says it carries out precise attacks on militants and tries to prevent harm to civilians, but its strikes often kill women and children.

According to the Israeli Ministry of Health, more than 42,000 Palestinians have been killed in the Israeli offensive. It does not distinguish between civilians and combatants, but says women and children account for just over half of the fatalities.

Northern Gaza was the first target of Israel’s ground invasion nearly a year ago and has suffered some of the worst destruction of the war, with entire neighborhoods in Gaza City and other cities in ruins. Most of the population fled after Israel issued evacuation orders in the early days of the war, but around 400,000 people are believed to have remained despite the harsh conditions.

Earlier this month, Israel again ordered a complete evacuation of the north, banning food aid from entering the area for about two weeks. That led many Palestinians to fear that the country had adopted a surrender-or-starve strategy proposed by former Israeli generals.

Israel allowed two aid shipments into the north earlier this week after the United States warned it could cut its military aid if its ally did not do more to tackle the humanitarian crisis.