The killing of 17-year-old Kian Delos Santos last week triggered rare protests against Duterte's controversial but popular campaign to eradicate drugs, with critics saying it highlighted rampant rights abuses by police enforcing the crackdown.
Since Duterte's term began 14 months ago, police have reported killing 3,500 people in anti-drug operations, with thousands more murdered over drug-related crimes and in unexplained circumstances.
Duterte and his drug war are backed by a large majority of Filipinos fed up with high crime and a slow-moving judicial system, according to national polls.
Police said the teenager was a drug courier who fired at them while resisting arrest. However CCTV footage emerged of two policemen dragging the unarmed boy away moments before he was killed.
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After his family held a wake for him at home, around 3,000 people including his classmates, neighbours, nuns, priests and human rights activists marched under cloudy skies to protest his killing, according to an AFP photographer at the scene.
"Kian is the name and face of the truth. We must not allow the truth to die with Kian's murder," said Father Robert Reyes, one of several Catholic priests who celebrated a church mass for the boy today.
The slow-moving procession snaked through narrow streets as participants, many wearing black ribbons, carried posters that read "Stop Killing the Poor", "Justice for Kian", and "Rehabilitation not Persecution".
The cortege stopped briefly for prayers outside a police station where the three officers who had arrested the boy were deployed. They have since been suspended.
Following their claims of Delos Santos being involved in the drugs trade, police told a public enquiry on Thursday that they only read about his alleged narcotics activity on "social media" after his death.
Amnesty International alleged in a report released in February that Philippine police shot dead defenceless people, fabricated evidence, paid assassins to murder drug addicts, and stole from those they killed or the victims' relatives.
It also said police were being paid by their superiors to kill drug suspects, and documented victims as young as eight years old.
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