JAMES LE MESURIER heard a calling that rouses very few. When Syria was plunged into civil war, he co-founded the White Helmets, who ran toward bombed-out pyres of concrete and attempted to save their neighbors and friends buried under the rubble. The White Helmets have operated only in the most dangerous zones in Syria, those cities outside the control of the government. Through a nongovernmental organization, Mayday Rescue, Mr. Le Mesurier helped train and equip the White Helmets, and he justifiably earned an unassailable reputation in Syria as a dedicated humanitarian.

The White Helmets, officially known as the Syrian Civil Defense, are first responders who rushed in to places where public services no longer function. They have saved more than 100,000 lives over the past five years. Mr. Le Mesurier, a former British Army officer, had the idea to train people in these war-ravaged communities to learn how to help themselves — to be ready when no one else would come. The group says, “Former bakers, tailors, engineers, pharmacists, painters, carpenters, students and many more professions besides, the White Helmets are volunteers from all walks of life. Many have paid the ultimate price for their compassion — 252 have been killed while saving others.” More than half died in strikes in which Syrian and Russian warplanes returned to a target to hit the rescue workers. They have been celebrated as true heroes in this awful war, and a Netflix documentary about their work won an Academy Award in 2017.

They have affixed GoPro cameras to their helmets and recorded valuable video of the attacks by Syria and Russia on schools, hospitals and civilians, documenting possible war crimes. They witnessed the Syrian air force attack that dropped nerve agents on Khan Sheikhoun in 2017 and the horrific aftermath, when some of the White Helmets themselves were contaminated trying to save the victims. For their courage, the White Helmets have been viciously savaged in disinformation campaigns by Syrian and Russian bloggers, bots and trolls, with the aim of deepening the fog of war or placing the blame on the opposition. On Nov. 8, the Russian Foreign Ministry wrote on Twitter, “The White Helmets’ co-founder, James Le Mesurier, is a former agent of Britain’s MI6, who has been spotted all around the world, including in the #Balkans and the #MiddleEast,” claiming he had a connection to “terrorist groups.” British officials said this was a smear and that Mr. Le Mesurier had never worked as a spy.

News accounts said Mr. Le Mesurier, 48, had suffered from stress and the pressure of it all. In Istanbul early in the morning of Nov. 11, he was found dead on the street near his apartment balcony, with fractures of the head and legs. Although preliminary reports say there are no signs of foul play, his death deserves a complete investigation given the risks he took and the enemies he had. His legacy of brave and selfless rescue efforts — in the collapsing darkness of falling concrete, resistant to the malevolent trolls — is towering indeed.

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