MANILA- The conviction of 3 policemen for killing teenager Kian Delos Santos can serve as a reminder to the police force to be "extra diligent" in following the law, Philippines' top cop said Thursday.

Philippine National Police (PNP) chief, Director General Oscar Albayalde said the "early resolution" of the case is a "clear indication that the justice system works in this country."

"This case can serve as a reminder for the rest of our personnel to be extra diligent in fulfilling the requirements of the law as we serve and protect our citizens," he said in a statement.

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Police officers Arnel Oares, Jeremias Pereda, and Jerwin Cruz were sentenced to reclusion perpetua, equivalent to 20 to 40 years in prison for the murder of Delos Santos.

• Kian's parents on cops' conviction: Justice is served

The 17-year-old's death in 2017 put the spotlight on President Rodrigo Duterte's war on drugs and even prompted a Senate investigation.

"Despite the conviction, we understand that legal remedies can still be sought by either of the party since the principle of due process works both ways," Albayalde said.

The police force also insisted that Delos Santos' case cannot be considered as an extrajudicial killing since those responsible were tried before a court.

“They were charged with murder, the fact that it was tried before the court how can you say that’s extrajudicial?” PNP spokesperson Chief Supt. Benigno Durana, Jr. said Thursday.

"There was never a policy in the PNP that we kill the drug suspects unless otherwise they put up a fight and the lives of our operating personnel are in danger," he added.

Albayalde, however, noted that the conviction would not hamper the PNP's fight against illegal drugs.

"This will not cause us to waiver a bit in our resolve to rid this society of the menace of illegal drugs," he said.

"We will be equally resolute in standing behind our front line personnel toiling in this war while fully upholding the constitutional rights of everyone," he added.

• Palace lauds conviction of cops in Kian's slay

-with a report from Maan Macapagal, ABS-CBN News