The panel’s two remaining members, Paulo Pinheiro of Brazil and Karen Koning AbuZayd of the United States, confirmed Ms. del Ponte’s resignation in a statement, and said they felt compelled to continue.

“It is our obligation to persist in its work on behalf of the countless number of Syrian victims of the worst human rights violations and international crimes known to humanity,” the statement said. “Such efforts are needed now more than ever.”

The Independent International Commission of Inquiry on the Syrian Arab Republic, as the panel is officially known, has produced a stack of reports that chronicle evidence of war crimes and crimes against humanity. It also has compiled names of perpetrators of the most serious crimes, which the panel once threatened to reveal. Its reports are an object lesson in how blatantly the laws of war have been broken, with no near-term prospects of accountability. The panel, at one point, called the Syria conflict “a proxy war steered from abroad.”

Only the Security Council has the authority to refer the conflict to the International Criminal Court. That is unlikely, as Russia, a permanent veto-wielding member of the Security Council, backs the government of President Bashar al-Assad and has directly intervened in the war. So too has the United States, in what it says is an attempt to rout the Islamic State from its strongholds along the Euphrates River.

The General Assembly, responding to the sense of inaction, established late last year a highly unusual office within the United Nations system to compile evidence of war crimes for prosecution in the future.