By Agence France-Presse
Duterte has vowed to pardon authorities involved in his bloody crackdown, but even he refused to defend the 2017 killing of Kian delos Santos in a dank Manila alley -- which helped spark rare protests against the campaign.
Police said the 17-year-old was a drug courier who fired at them while resisting arrest. However, CCTV footage showed two of the policemen dragging the unarmed boy moments before he was shot dead.
Delos Santos' family erupted in tears in the cramped northern Manila courtroom after the men were convicted of murder and sentenced to reclusion perpetua, which carries a minimum of 20 years behind bars.
"I feel so happy because this proves that my son was innocent and was never involved in drugs," Delos Santos' mother, Lorenza, told reporters.
"(Policemen) can be jailed for life if they do not stop their abusive practices," she added.
Drug war critics hailed the conviction as an example of justice and accountability, which they said have been rare since Duterte unleashed the campaign to rid the Philippines of narcotics in 2016.
Since then police say they have killed nearly 5,000 alleged drug users and pushers who fought against arrest, while rights groups say the true toll is at least triple that and may amount to crimes against humanity.
- 'Who gave the orders?' -
Carlos Conde, Philippines researcher for Human Rights Watch, told AFP: "This is a warning to the Philippine National Police that they better follow due process and respect the rights of suspects."
However, Duterte's spokesman Salvador Panelo also welcomed the ruling as he gave assurances the president opposed "intentional killing".
"It shows that this country has a robust judicial system," he added.
Duterte's government has argued a preliminary probe of the drug war killings launched by the International Criminal Court is unjustified because the nation's justice system is functioning.
Rights advocates agreed the decision was important, but noted that it only involved low-ranking policemen.
"Who gave the orders? Was this part of a policy? These questions remain unanswered," rights lawyer Romel Bagares told AFP.
Duterte and his drug war are backed by many Filipinos fed up with high crime rates and a slow-moving judicial system.
But the death of Delos Santos, as well as of two other Manila teenagers accused of robbing a taxi driver, triggered rare street protests in 2017 and highlighted concerns about police abuse.
Days after the killing Duterte said in a speech: "It was really bad. That was really not performance of duty. Do not commit a crime".
It led to Duterte briefly suspending police participation in the drug crackdown for a second time.
The first occasion was in January last year after narcotics police officers were arrested for the kidnapping and murder of a South Korean businessman in 2016.
However, in both instances the police were reinstated in the campaign without major reforms.