The U.N. human rights chief asked Philippine authorities Tuesday to investigate President Rodrigo Duterte for murder after he claimed to have killed people in the past and also to examine the “appalling epidemic of extra-judicial killings” committed during his anti-drug crackdown.

Philippine judicial authorities “must demonstrate their commitment to upholding the rule of law and their independence from the executive by launching a murder investigation,” U.N. High Commissioner for Human Rights Zeid Ra’ad Al Hussein said, adding it’s “unthinkable for any functioning judicial system not to launch investigative and judicial proceedings when someone has openly admitted being a killer.”

Since taking office in June, Duterte has obsessively overseen the crackdown on illegal drugs that has left more than 6,000 people dead. Philippine government officials have defended police actions during the crackdown, and the president has met past such calls with angry tirades.