MANILA, (AFP) -- Philippine President Rodrigo Duterte’s office vowed on Sunday  there would be no cover-up or whitewash in the investigation into a South Korean’s murder by police.

The kidnapping and killing of the businessmen has fuelled fears about widespread abuse by officers as they prosecute Duterte’s deadly anti-drug war.

The businessman disappeared from his home in Angeles City north of Manila last October.

Police from a special anti-drug unit abducted him under the guise of a raid on illegal drugs.

A policeman then strangled him inside Camp Crame, the national police headquarters in Manila, the Justice Department said last week.

“We are outraged by the abduction and slay of a South Korean executive inside Camp Crame,” said Duterte’s spokesman Ernesto Abella.

 “We assure everyone that there will be no whitewash or cover-up. We will not tolerate abusive, errant policemen who betray the organization.”

The kidnappers demanded a ransom from the victim’s wife and she initially paid five million pesos ($100,000), thinking he was still alive, authorities said last week when they first announced details of the police officers’ involvement.

The policemen for months led the wife to believe her husband was alive but he had been in fact killed on the day he was abducted, investigators said.

The officers involved were from a task force focused solely on illegal drugs and stationed at the sprawling Camp Crame.

The incident has shocked and angered the South Korean government, with Foreign Minister Yun Byung-Se demanding those behind the crime be brought to justice.

The police have come under intense scrutiny as the frontline troops in Duterte’s efforts to eradicate illegal drugs in society, with human rights groups accusing them of mass extrajudicial killings.

Police have reported killing 2,250 drug suspects since Duterte assumed office, with 3,710 others murdered by unknown suspects who at times have left signs at the crime scenes accusing their victims of being drug dealers or addicts.

Duterte has repeatedly promised to protect police from prosecution if they are charged with murder for killing a drug suspect, leading to fears corrupt officers feel they have a green light to commit crimes in the name of the drug war.