The body of 22-year-old pedicab driver Eric Sison lies in a coffin in a Manila slum with a chick pacing across his coffin, placed there in keeping with a local tradition to symbolically peck at the conscience of his killers.

Mobile phone video footage circulating on social media purports to capture the moment Sison was killed last month when, according to local officials, police were looking for drug pushers in the Pasay township of the Philippines' capital.

A voice on the video, recorded by a neighbour according to newspaper reports, can be heard shouting "Don't do it, I'll surrender!". Then there is the sound of gunfire.

A poster near the coffin demands "Justice for Eric Quintinita Sison". A hand-painted sign reads: "Overkill - Justice 4 Eric."

These are rare tokens of protest against a surge of killings unleashed since Rodrigo Duterte became president of the Philippines just over two months ago and pledged to wage war on drug dealers and crush widespread addiction to methamphetamine.

Very little stands in the way of his bloody juggernaut.

Last week the number of people killed since July 1 reached 2,400: about 900 died in police operations, and the rest are "deaths under investigation", a term human rights activists say is a euphemism for vigilante and extrajudicial killings.

Indeed, Duterte may intensify the crackdown after 14 people were killed on Friday in a bomb attack at a market in his hometown, Davao. Police blamed the Abu Sayyaf, an ISIL-linked group Duterte has vowed to destroy, but his war on the drug trade is making enemies elsewhere and the attack quickened rumours of a plot to kill him.

Duterte's office did not immediately respond to a Reuters request for comment on this report.

Police overload, public fear

Interviews reveal that the police's Internal Affairs Service (IAS) and the Commission on Human Rights (CHR) are so overwhelmed by the killings that they can investigate only a fraction, and there is scant hope of establishing many as unlawful because witnesses are too terrified to come forward.

Philippines: ‘State of lawlessness' declared after deadly Davao attack

Meanwhile, the immense popularity of Duterte's crusade and a climate of fear whipped up by the blood-letting have together silenced dissent from civil society.

Hardly anyone turned up at candlelight vigils in Manila recently to protest against extrajudicial killings.

Anxious reminders by the Catholic Church of the commandment 'thou shalt not kill' make few headlines in the predominantly Catholic country, with newspapers preferring to carry breathless accounts of the latest slayings.

Duterte has delivered withering attacks on his chief critic, Senator Leila de Lima, accusing her of dealing in drugs herself and having an affair with her driver.

As for critics abroad, Duterte pours scorn on them in language laden with curses.

He lambasted the United Nations after it criticised the surge in killings and he turned down a meeting with UN Secretary General Ban Ki-moon at a summit in Laos this week.

Duterte will meet Barack Obama in Laos on Tuesday, although he has made it clear in advance that he will take no lecture on human rights from the US president, when in the United States, he alleged, "black people are being shot even if they are already lying down".

No witnesses

Chief Superintendent Leo Angelo Leuterio, who heads the IAS, said that with only about 170 investigators nationwide, the unit can deal with just 30 percent of the roughly 30 cases coming in daily.

"Our resources are breaking at the seams," said Leuterio.

The CHR, for its part, is looking at just 259 of the 2,000-plus killings since July 1, and its forensics team of 14 is swamped. The commission says its biggest obstacle is that witnesses are hard to find.

On August 29, police told reporters that they had opened fire that night on a drug suspect in Tondo, a dirt-poor and densely populated district of Manila.

A Reuters reporter looked into the suspect's one-room home and saw a mattress splattered with blood. He asked a neighbour how many shots had been fired, but the man replied: "Sorry, my friend. I didn't hear a single shot," and walked away.