A jailed critic of Philippine leader Rodrigo Duterte on Saturday praised police who alleged in a Reuters report that officers received cash for executing drug suspects, and said an international criminal case should be filed against the president for crimes against humanity.

Senator Leila de Lima described as "brave and honourable men" the two senior police officers, one still in service and the other already retired, who made the allegations about the conduct of officers during Duterte's bloody war on drugs. 

De Lima said the two officers, who spoke to Reuters on condition of anonymity, had given "testimonial proof that the extrajudicial killings are indeed state-sponsored and carried out upon direct orders of the president."

Philippine National Police (PNP) chief Director General Ronald dela Rosa on Friday challenged the two officers to come out and face him, according to GMA News online.

Close to 9,000 people have died since Duterte took office and promised an unrelenting campaign to rid the Philippines of illegal narcotics. About a third were killed in anti-drug operations in which officers said the victims had violently resisted arrest.

Many other deaths were blamed on mysterious vigilantes who killed dealers and users, or homicides that could be unrelated to drugs. Police deny any involvement in those killings, most of which they say remain under investigation.

The two policemen who spoke to Reuters said PNP officers carried out most of the killings attributed to vigilantes.

"It is just a matter of time before all of the truth comes out in all its horrifying detail, of how a president took hold of a nation's consciousness to promote social cleansing as a final solution to the nation's problems," De Lima said.

De Lima last year led a Senate probe into alleged summary killings during Duterte's anti-drugs campaign but has since been detained on charges of involvement in the drugs trade in prisons when she was justice minister in the previous administration. She says the charges are trumped up.

De Lima said there should be no doubt there was sufficient cause to file an international criminal case for crimes against humanity against Duterte, Dela Rosa and other police commanders and high ranking cabinet members and lawmakers.

One of the two policemen, a retired intelligence officer, authored an unpublished 26-page report that provides granular detail on the alleged methods deployed in the drug war, as well as the campaign's masterminds and perpetrators. The report, which said it is based on the accounts of 17 serving and former officers, does not contain any documentary evidence.

The president's office has said there was "no such report," and that police were "not in the business of hiring assassins."

It also called on the two officers to make their complaints publicly and under oath.

A Reuters spokesperson said: "Our reporting was fair and accurate and we stand by it."

PNP chief dela Rosa was quoted saying the two officers were "cowards".

"If they have balls to face the media and make accusations like that, they should also have balls to face their commanders," GMA quoted him telling reporters.

Source: Timesofoman