A Filipino lawyer formally asked the International Criminal Court on Monday to charge President Rodrigo Duterte and 11 officials with mass murder and crimes against humanity over the extrajudicial killings of thousands of people in the Philippines over the past three decades. The I.C.C. should promptly open a preliminary investigation into the killings.

The lawyer, Jude Josue Sabio, filed the complaint in his own name, but he also represents two men who have publicly said they were paid members of the death squad that Mr. Duterte set up in Davao City when he was the mayor to hunt down drug dealers. After he was elected president last year, Mr. Duterte took the killing campaign nationwide, effectively declaring an open season for police and vigilantes on drug dealers and users. In all, Mr. Sabio said in the 77-page filing, more than 9,400 people have been killed, most of them poor young men, but also bystanders, children and political opponents.

Mr. Sabio is not the first to accuse Mr. Duterte of mass killings — so have Human Rights Watch, in 2009; Amnesty International, this January; and some brave Filipino politicians. The I.C.C. chief prosecutor, Fatou Bensouda, declared last October that the court was “closely following” developments in the Philippines.

There are reasons why the I.C.C. might be reluctant to go after Mr. Duterte. He is enormously popular with many Filipinos, for whom narcotics are a major scourge.