Mr. Batsh told friends in Malaysia that he had narrowly avoided an attempt on his life while still living in Gaza. In 2014, his uncle, Tayseer al-Batsh, the Gaza police chief, was nearly killed by Israeli airstrikes. Eighteen members of the Batsh family died in those raids.

But Mr. Batsh did not dwell on his family’s tragedy, his friends in Malaysia said, though he wrote social media posts criticizing Israel over the conflict with Gaza. “Most everyone in Gaza has lost a member of the family,” said Hafidzi Mohammed Noor, chairman of Humanitarian Care Malaysia, a charity that provides humanitarian assistance to Gaza. “For him, for all the Palestinians here in Malaysia, this is normal.”

Over the weekend, a mourning tent was set up in the Jabaliya refugee camp in Gaza, where Mr. Batsh grew up. Ten masked members of the Qassam Brigades, Hamas’s armed wing, were stationed in front of the tent, a positioning that usually denotes the death of a top fighter.

Banners hung in the tent described Mr. Batsh as an “engineer commander” for the Qassam Brigades and “our martyr to God.” Another relative of Mr. Batsh’s was said by family members to be a commander in Islamic Jihad, a separate militant group that operates in Gaza.

On the day he was killed, Mr. Batsh was supposed to travel to Istanbul to attend an academic conference. One Middle Eastern intelligence official, however, said that Hamas’s efforts to cultivate its scientists living abroad were directed from Istanbul, and that Mr. Batsh was scheduled to meet with the head of the unit, Maher Salah, upon arrival in Turkey.

Western and Middle Eastern intelligence officials said that Mr. Batsh may have been involved in negotiating North Korean arms deals through Malaysia. Egypt recently seized a shipment of North Korean communications components used for guided munitions destined for Gaza, they said. One intelligence official said that Mr. Batsh had helped mediate the deal.

Although such weapons are under international sanctions, the United Nations said in a report last year that a shell company run by North Korea’s intelligence agency had been hawking military-grade communications systems from Malaysia.