Mohammed Sinwar, a Hamas leader, was claimed to have died in 2014.
However, Israeli spies now believe he is alive and that he helped mastermind the October 7 attacks.
They believe he has spent years living in Hamas' labyrinth of tunnels under the Gaza Strip.
A Hamas leader who was pronounced dead years ago is now believed to be alive and to have helped mastermind the October 7 attacks, Israeli intelligence says, The Telegraph reported.
Mohammed Sinwar, the younger brother of Hamas' leader in Gaza Yahya Sinwar, was pronounced dead by the militant group in 2014, with the group even releasing an image of him lying in a blood-soaked bed.
However, Israeli spies are now said to believe that his death was faked and that he had been living in Hamas' "spider's web" of tunnels under Gaza for years, sources close to Israeli intelligence said.
"He was 100 per cent one of the core team who planned October 7," a former Mossad counter-terror chief told The Telegraph.
Hamas' surprise terror attack on Israel saw militants attack by air, land, and sea, leading to the deaths of around 1,200 people in Israel and the taking of around 240 hostages.
"In the military leadership he's very important," the former Mossad chief said about the younger Sinwar. "He's around number seven on the wanted list, alongside the likes of Mohammed Deif, Marwan Issa and Tawfiq Abu Naim. He's an important figure and he's still alive for sure."
The younger Sinwar specializes in helping secure the release of Palestinians who are in Israeli prisons through border infiltration and kidnappings, Ronen Solomon, an independent intelligence analyst, told The Telegraph.
Solomon said that Sinwar survived six assassination attempts over the last two decades and that he had limited his movements to protect himself.
He has never been seen in public since he was pronounced dead, and Gazan residents would likely not even recognize him now, he added.
The IDF hinted in a post on X, formerly Twitter, that it was once again targeting Mohammed Sinwar, writing that soldiers had searched an office linked to him and found "military doctrine documents."
Mohammed Sinwar was one of the earliest members of the military arm of Hamas, having previously worked in administrative roles, per The Telegraph.
The ex-Mossad chief said that Sinwar also played a key role in securing his older brother's release from an Israeli prison in a 2011 prisoner exchange.
Yahya Sinwar is Israel's most wanted target. Israel's defense minister Yoav Gallant said earlier this week that the older Sinwar, who was once saved by Israeli doctors when he was in prison in Israel, was surrounded in a bunker. Officials have described him as a "dead man walking."
Yahya became the leader of Hamas in Gaza and a member of its political bureau in 2017, according to the think tank the European Council on Foreign Relations. He is believed to be one of the key figures linking Hamas' political bureau with its military faction, the think tank added.
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