Philippines President Rodrigo Duterte apologized to South Korea on Thursday after policemen killed one of its citizens, then said he wanted to hang rogue police and send their heads to Seoul.

He called again for the death penalty to be reinstated so that he could hang 20 criminals a day.

Duterte promised the toughest punishment for those behind the kidnapping and killing of businessman Jee Ick-joo inside the national police headquarters in October.

“I will see to it that they are sentenced to the maximum,” he said of the policemen. “You give that power to me back again, I will execute them… I’ll hang them in one day, 20 of them – 20 a day.”

He added: “You sons of bitches, you policemen. You will suffer. I can maybe send your heads to South Korea.”

The death of the South Korean comes as the Philippine police face growing criticism from rights groups and some lawmakers, who say cover-ups and abuses of police power are rampant.

Duterte’s critics, however, say he is to blame for creating a culture of impunity by promising to protect police on the front lines of his war on drugs.

The police accused of kidnapping and killing Jee were anti-narcotics officers.

Capital punishment has been a priority for Duterte, whose allies introduced a death penalty bill in Congress on June 30 last year, the same day as his inauguration.

The draft, which is still being debated, says existing laws are no deterrent and had “emasculated” the criminal justice system. The death penalty was repealed in 2006 following pressure from church groups.

A Senate investigation into Jee’s killing began on Thursday with police chief Ronald dela Rosa, a close ally of Duterte, saying he was “overcome by shame”.

“All indications point to an elaborate web of criminal activity by some police personnel operating under the cover of legitimate police operations,” he told the hearing.