A solemn crowd gathered in the National Cathedral in Washington, D.C., on Thursday to remember the seven staffers for the aid group World Central Kitchen who were killed in a drone attack in Gaza, sparking a wave of renewed outrage at the Israeli military.

José Andrés, the celebrity chef and founder of the organization, mourned the loss of seven members in the April 1 Israeli strike, people he called "the best of humanity."

Recounting the workers' lives and their paths to joining the organization, he choked up. One staffer, Jacob Flickinger, a 33-year-old dual citizen of the U.S. and Canada, was called "Tío Jacob" by children in Acapulco, where he volunteered aid in the wake of a hurricane, Andrés said. Another, Damian Soból, had a street named after him in Turkey in honor of his efforts to help after an earthquake.

Saifeddin "Saif" Abutaha, a 25-year-old Palestinian whose family flour business became the aid group's headquarters in Gaza, was texting his mother to ask whether she was asleep when he was killed, Andrés said.

Andrés reiterated his demand for an investigation into the workers' deaths. "I know we all have many unanswered questions about what happened and why. There is no excuse for these killings. None," he said. "The official explanation is not good enough and we still demand an investigation into the actions of the IDF. Even one innocent life taken is one too many."

He urged "leaders to lead by the same standards" as the humanitarian workers. "The fate of the many cannot be decided by the hateful and divisive actions of the few," he said.

The celebration of life was held under the sweeping ceilings and stained glass windows of the cathedral and was punctuated with musical performances, including from famed cellist Yo-Yo Ma. Second Gentleman Doug Emhoff, Deputy Secretary of State Kurt Campbell and Sen. Chris Van Hollen attended the ceremony.

Three faith leaders of the Washington area – Imam Talib Shareef, Rabbi Susan Shankman, and Archbishop Wilton Cardinal Gregory – offered prayers in memory of the workers.

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Drone struck aid convoy that coordinated movements with IDF

The group of staffers – which included British citizens John Chapman, 57, James Henderson, 33, and James Kirby, 47, and Lalzawmi Frankcom, 43, of Australia – were killed after an Israeli drone struck their convoy carrying aid through a deconflicted zone in Deir al-Balah in the central Gaza Strip.

The drone hit the group as it left a warehouse after it unloaded more than 100 tons of aid in two armored trucks branded with World Central Kitchen's logo. The convoy had informed the IDF of its movements, according to the aid group. The organization halted its humanitarian aid efforts in Gaza – previously one of the largest in operation in the war-torn enclave – in response to the workers' deaths.

The deaths fueled outrage at the IDF's conduct in its ongoing siege in Gaza, where more than 34,000 Palestinians have died since Israel launched a sweeping military operation in response to Hamas' surprise attack on Israeli border communities on Oct. 7. The U.N. said the World Central Kitchen's staffer deaths brought the number of aid workers killed in the conflict to "at least" 224.

President Joe Biden expressed outrage over the incident, saying Israel had not "done enough to protect aid workers" in Gaza. Biden spoke with Andrés and called the workers' deaths a "tragedy" that demanded a speedy investigation.

The incident also led to a rare apology from Israeli Prime Minister Benjamin Netanyahu, who called the attack unintentional. An internal investigation by the Israeli military called the strike a "grave mistake" and said those who struck the convoy believed it carried Hamas operatives, according to an IDF statement.

Two IDF officers were fired for their involvement, a move WCK said was an "important step forward" but insufficient. The report, the organization said, showed that the IDF did not follow its own "protocols, chain of command and rules of engagement" when it "deployed deadly force."

Cybele Mayes-Osterman is a breaking news reporter for USA Today. Reach her on email at [email protected]. Follow her on X @CybeleMO.