Like other news organisations, Israel does not let the BBC cross into Gaza except on rare, supervised trips with the army.
In the ruins of Khan Yunis, the birthplace of Sinwar, Palestinians interviewed for the BBC by local trusted freelancers were defiant. They said the war would go on.
"This war is not dependent on Sinwar, Haniyeh, or Mishal, nor on any leader or official," said Dr Ramadan Faris.
"It's a war of extermination against the Palestinian people, as we all know and understand. The issue is much bigger than Sinwar or anyone else."
Adnan Ashour said some people were saddened, and others were indifferent about Sinwar.
"They're not just after us. They want the entire Middle East. They're fighting in Lebanon, Syria, and Yemen... This is a war between us and the Jews since 1919 over 100 years."
He was asked whether the death of Sinwar would affect Hamas. "I hope not, God willing. Let me explain: Hamas is not just Sinwar... It's the cause of a people."