It’s approaching 5am on a Sunday morning before Christmas, and in the Santo Niño district of Pasay city, Metro Manila, Domingo Mañosca is already up and about. His heavily pregnant wife, Elizabeth, is still fast asleep. Sprawled beside her, in a tangle of little arms and legs, lie their three children: five-year-old Francis wedged up against their shanty’s plywood wall; their eldest, nine-year-old Juliebeth, small for her age, curled up round her 18-month-old sister, Erika, the baby who never stops smiling.

Their second-floor room is rough-hewn, windowless, pokey, nailed together in a patchwork of scavenged shards of planking and ply. All five sleep together on rattan mats, spread over a lino-covered wood platform; none has ever known creature comforts. Upstairs, Domingo’s brother, his wife, and their two children are crammed into another room just off the shared space where they all live and cook. His widowed mother, Maria, also sleeps there.

To make some kind of living, Domingo rents a sidecar, a bicycle-taxi designed for two passengers – but which usually carries more, whole families, sometimes, in addition to their bags and boxes stacked high. Often he doesn’t get back until late; sometimes he works through the night. The early mornings belong to him, though; Domingo slips out, descends three makeshift ladders into the darkness of the alleyway below, and wends his way to the stalls to buy a coffee. He has to be out on the bike by seven.

Renting it costs him 60 pesos (90p) a day. After that, the money is all his. One trip earns around eight or 10 pesos. On a good day, he can clear 140 after the cost of the rental, but that’s on a good day. He would love to have his own secondhand sidecar, but at 5,000 pesos, it’s nothing more than a pipe dream.

Duterte’s drugs war in the Manila slums is increasingly seen as a war on the poor. Photograph: Noel Celis/AFP/Getty Images)

In recent months, Domingo has taken the odd toke of shabu – methamphetamine – to help him pedal harder for longer; it messes with your head, but it’s like downing a hundred cups of coffee at once. Loads of his fellow sidecar boys do it, too; it’s pedi-cab turbo, poor man’s cocaine. When he needed to really push himself, to earn a bit extra, like when one of the children was ill and he had to buy medicine, shabu seemed heaven-sent. Yet the price of a hit had rocketed when Rodrigo Duterte – the tough-talking candidate he had voted for in May 2016 – became president and launched a drugs crackdown. The small plastic sachets were still affordable, though; and smoking it had always paid off: afterwards he wouldn’t need to sleep for two days. But now his shabu nights were over. The barangay kapitan, an elected official at the head of the community, had been compiling lists of local users. Somehow, Domingo had ended up on the “watch list” and last week he’d had a warning visit from the cops. Word was he had been shopped by a dealer.

Wanting to do the right thing, and after talking it over with Elizabeth, he had decided to go down to the police station and sign their “surrender book” undertaking not to touch the stuff again – and he hadn’t. In a neighbourhood where so many were at it, he was one of the few who had fessed up. Better safe than sorry, he had thought. Supposedly, signing the book would provide him with state-sponsored rehab, although that had yet to happen.

The surrender experience had made him feel a bit anxious though, and his wife, too, especially when they had heard from a neighbour that a stranger had since been asking around for him.

Santo Niño is a densely packed neighbourhood in the heart of Metro Manila, a conurbation in the Philippines made up of 16 cities and one municipality. The district is a maze of alleyways, some just shoulder-width; its residents live on top of one another in a heap of impoverished humanity, focused on the art of survival. For much of the year, this warren is insufferably hot and airless, but December is cool and bearable, and at this time of day, before dawn, it’s still quiet, too.

Returning with his two plastic bags of sweet, milky coffee, Domingo, in the light of a naked 40-watt bulb, grabs a screwdriver and starts fiddling with the family’s broken DVD player. He’s good with electronics, and he had promised Elizabeth he would fix it. It’s still only just gone five and Domingo is squatting on the edge of the raised platform, beside his slumbering family.

Manila protesters march against the drugs war killings. Photograph: Jes Aznar/Getty Images

As he sucks a warm strawful of coffee, there’s a knock on the door at the foot of the ladder. “Sino yan?” he calls. Who’s there?

No answer. Again, a knock; again no answer. At this point, Domingo Mañosca has roughly two minutes left to live.

From just behind him, there is a brief scraping sound, metal on wood. Then, before he can even wheel round, a shot. There were two, in fact. Domingo heard the first one, which missed him, but he does not hear the second.

Elizabeth Navarro opens her eyes in blind panic and, as she does, her husband lands heavily on top of Juliebeth’s tiny frame. The left side of his face has been blown off. She recoils in horror. Her first thought is for her daughter, pinned beneath him, and as his hot, sticky blood begins to ooze over everything, she wrenches the little girl from under Domingo’s heavy, limp body. Emerging, smeared in her father’s dark blood, Juliebeth stares as she takes in the scene.

Erika, the happy baby, is screaming, and as Elizabeth scoops her up, her eyes dart to five-year-old Francis, lying strangely motionless. He, too is drenched in blood, and, fighting a rising hysteria, she realises it isn’t blood from his mortally wounded father. It is his. Handing the baby to Juliebeth, she reaches for him just as her brother-in-law, Roberto, bursts through the door. The gun had been fired through the gap in the wall just behind Francis, and the first shot had hit Elizabeth’s only son in the head. Yet the little boy is still breathing; perhaps, she hopes, the bullet has just grazed him. She thrusts Francis at his uncle, who, realising there is no hope for his brother, clambers back down the ladder and races on his own rented bicycle sidecar to Pasay city general hospital, his wounded nephew unconscious on the passenger seat beside him.

At a few minutes past 5am on that Sunday, just before Christmas, Domingo Mañosca, 44, sidecar “boy”, breadwinner, Duterte-supporter, father, husband, and sometime shabu user, became another statistic in the president’s war on drugs, summarily executed inside his own home by an unknown killer. Two hours later, Elizabeth would learn that her little Francis was now also just a statistic. Roberto returned alone and despondent.

Police inspect a crime scene in Pasay city. Photograph: Jes Aznar/Getty Images

Time magazine published a photo-essay on Duterte’s drugs war by the renowned photojournalist James Nachtwey. The last picture in his devastating black-and-white collection shows Elizabeth, her belly swollen, sitting barefoot on the floor of a Pasay funeral parlour. In Philippine funereal tradition, it’s considered bad luck for a woman who is pregnant to attend a wake or look upon the dead, but Elizabeth had little choice. Her expression, as she observes her lonely wake, is the quintessence of hopelessness. The sides of her mouth are cast down in an almost clown-like demeanour and she is gazing vacantly at a distant point, several light years away. Two white coffins containing Domingo and Francis, one big, one pitifully small, rest on gurneys. Just visible in Nachtwey’s picture are two tiny yellow chicks, placed on the glass window in the coffins’ lids to peck at grains of rice. This widely practised superstition is reserved for murder victims.

The pecking chicks symbolise the pricking of the unknown killer’s conscience so as to hasten justice. The custom has persisted despite the impunity enjoyed by the henchmen of Duterte’s drugs war. The two coffins have ornate scalloped handles and embossed designs down their sides. The cheapest coffin costs four times what Domingo’s pipe-dream sidecar would have. A low-end cremation package comes in at 35,000 pesos. About £520.

A few days later, the freshly cremated ashes of father and son are interred together at Pasay city cemetery, a graveyard as chaotic and crowded as the slums its residents had left behind. There have been so many extrajudicial killings in Pasay that local reporters have sardonically rechristened it “Patay city”: City of the Dead. The municipal cemetery has been filling up fast since Duterte Harry, as his nom de guerre has it, came to town; a whole section has been unofficially renamed the Duterte compound”, a stack of high-rise tombs in a four-storey concrete matrix along the back wall of the cemetery.

Because so many families have proved unable to cover the prohibitive costs of coffins and cremation, the Catholic Church has set aside a special fund at the famed local Baclaran Redemptorist Catholic Church, Our Mother of Perpetual Help. Many graves have no names at all and are simply numbered. No 116, scratched into the wet concrete with a stick. No 265. These are the unknown drugs war dead, the doomed youth who die as cattle.

Killing spree ... Duterte said children caught in the crossfire of his war on drugs were ‘collateral damage’. Photograph: Bullit Marquez/AP

It’s a dreary, wet Sunday, several weeks later. Elizabeth has just had her baby, a boy she’s called Franc Dominic, and I’ve gone to Pasay to see them. In these labyrinthine squatter colonies, Duterte’s war on drugs is increasingly seen as a war on the urban poor. Confronted by the scale of the slums, and the sheer number of people crammed into them, it’s hard to believe government statistics claiming that in the Metro Manila conurbation, fewer than one in 10 people live in extreme poverty. There is even a Tagalog slang word for food scavenged from other people’s rubbish: pagpag, a survival staple. Garbage chicken, beef from bins, assorted delicacies of discarded scraps; washed, recycled, bagged, and sold from hand-pulled pagpag carts. That’s how poor these people are. In the national capital alone, maybe a million Filipinos are unable to afford to feed their families or themselves. And it’s their communities that have been targeted by and suffered the most in police anti-drug operations.

Elizabeth speaks some English, but a Filipino journalist friend has come with me to translate from Tagalog. We talk for a bit about her husband, Domingo. It turns out he had spent four years in jail for robbery in the past. Local newspapers had reported that he had been a known drugs pusher, citing the district police chief as their source. Elizabeth denies this, although she readily admits he smoked it. “Yes, he used shabu. If he had to work all night, to earn more, that’s when he’d use it. It’s a huge problem here. It’s like a virus. But killing people isn’t the answer. If he hadn’t been so honest and surrendered, he would probably still be alive,” she says, looking down at her baby. “He signed his own death warrant.”

The police had come after the shooting, she tells me, but not one witness came forward. No one has been arrested. “We are all still afraid,” she says. “We’re worried that whoever shot my husband might come back. I just hope that what happened is enough, that they got what they wanted.”

After the double murder, it was fear that had spread through Santo Niño, like a virus.

Elizabeth struggles to even find the money for baby formula. She’s renting out the room Domingo and Francis were killed in for 2,000 pesos a month; it’s what Domingo used to earn in a fortnight. She looks drained, and gaunt; still numb from what she has been through. Aged 29, with three children, no husband, and no income, the future must look bleak indeed. So, instead, Elizabeth talks of her memories of her naughty five-year-old son. “Francis was such a happy little boy,” she says.

Duterte made international headlines when, a few months into his presidency, he described the deaths of children caught in the crossfire of his war on drugs as “collateral damage” – a phrase associated with the unfortunate consequences of war.. It was Duterte who called this a “war”. No one else had ever really seen the need. And, in the slums of Manila, his war is one-sided.

Francis Mañosca was not the first child collateral, and there have been scores of other children killed since on this battlefield.

The funeral of 17-year-old schoolboy Kian Loyd delos Santos, shot dead by police, turned into of the biggest demonstrations yet against brutal Duterte’s policy. Photograph: Ezra Acayan/NurPhoto via Getty Images

Operation Double Barrel, as the police operation in Duterte’s war on drugs is known, has left innocent bystanders lying in pools of blood; there have been cases of mistaken identity, and the licence to kill provides perfect cover for personal vendettas. But the rising number of dead children has begun to trigger particular alarm. Ten days after Francis was shot and killed, 12-year-old Kristine Joy Sailog was shot dead in the car park of her local church, just south of Manila, as she left Christmas mass with her mother. She was hit in the chest by a single round, allegedly fired by masked men on a passing motorcycle. They had been aiming at somebody else, who was also killed. The Children’s Legal Rights and Development Center reported that, in the first six months of the drugs war, at least 31 children were shot dead – the youngest a four-year-old girl. Other children, like Juliebeth, have been frontline witnesses to the murder of their friends and family members. Large numbers of children have been orphaned and left without carers or a breadwinner.

The murders of three teenagers in August and early September 2017 proved to be a benchmark moment, jolting a country that had become inured to killing into taking notice. The teenagers were among 96 people killed in Manila in the space of a few days as part of what the police called a “one-time, big-time” assault on alleged dealers in the capital region. Two of the three were under 18, which brought to at least 54 the number of children killed in the drugs war.

The first to die was 17-year-old Kian Loyd delos Santos, in Caloocan city, on the northern fringes of metropolitan Manila. Police claimed he was a meth dealer who had fired at cops during a raid; they had acted in self-defence, they said, after he had opened fire on them. But, for once, CCTV footage emerged that told a different story. It clearly showed two plainclothes police officers dragging the teenager away before he was shot dead in a rubbish-strewn alleyway, his body dumped next to a pigsty. He was found with a hole in his head and another gunshot wound to his torso, grasping a pistol in his left hand. His parents said their son was right-handed. Justice secretary Vitaliano Aguirre II described the killing as “an isolated case”.

The Caloocan funeral of Delos Santos turned into one of the biggest protest marches yet against Duterte’s war on drugs, with more than 5,000 people, including nuns, priests, the families of 20 other drugs war killings, and hundreds of children, chanting “Justice for Kian, justice for all!” The public backlash over his killing resulted, in January 2018, in the filing of murder charges against the three police officers who had lied about how he died. This was hailed by human rights groups as a rare instance in which the Philippine justice system has taken genuine steps to prosecute anyone for murders linked to Duterte’s war on drugs.

Kimberly Sailog mourns her 12-year-old daughter, Kristine, who was killed by a stray bullet in a church car park. Photograph: Mark R. Cristino/EPA

But the killing spree that Duterte ushered in as president is not the first time Filipino children have been exposed en masse to extreme violence. In Davao city, during Duterte’s time as mayor, children were directly targeted. More than 130 of them were among 1,400 killed between 1998 and 2015. The perpetrators of these unsolved murders were euphemistically labelled “unknown vigilante killers”. But everybody knew this to be the handiwork of what was ubiquitously referred to as the “Davao Death Squad”. Many of the murdered children were street-kids; others were petty criminals, some were addicts.

In the first six months of Duterte’s presidency, more than 26,000 under-18s, allegedly involved in using, selling, or transporting drugs, surrendered to police, according to Philippine national police statistics. On 30 June 2016, immediately after his inauguration as president, Duterte paid a visit to Tondo, the biggest slum in Manila. There, addressing a crowd of around 500 people, he said: “If you know of any addicts, go ahead and kill them yourself, as getting their parents to do it would be too painful.”

From early on, mental health workers warned of the psychological impact of the drugs war, particularly on children. They talked of how prolonged exposure to images of extreme violence could lead to them exhibiting violent behaviour, aggression, and delinquency, and, as they grew older, crime. “Violence can beget violence,” child psychologist Dr Joanna Herrera told a Philippine national newspaper. “Overexposure can also lead to desensitisation, especially for children who are more malleable … It is not just about the violence, but the tacit approval of it.”

Anecdotally, Duterte’s expletives and profanities are now being imitated in school playgrounds the length and breadth of the archipelago. There are many who are concerned about the long-term damage. Trust in the Philippine national police has been seriously undermined. Moral values have been eroded. In Manila, a Catholic priest who has worked at the sharp end of the war on drugs related an anecdote about a family he knew in which a child told his father how angry he was with his teacher.

“I want to kill him,” the boy had said.

Extracted from Duterte Harry: Fire and Fury in the Philippines by Jonathan Miller, published by Scribe (£14.99) on 14 June. To order a copy for £12.74 go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99