A Philippine court on Thursday sentenced three police officers to up to 49 years in jail for the murder of a 17-year-old high school student, the first to be convicted in President Rodrigo Duterte's drug war.

The Caloocan City regional trial court declared the three police guilty for the killing of Kian Lloyd delos Santos in August 2017 in a dark, trash-filled alley in a northern suburb in the capital Manila.

"A shoot first, think later attitude can never be countenanced in a civilized society. Never has homicide or murder been a function of law enforcement. The public peace is never predicated on the cost of human life," said the ruling by Judge Roldolfo Azucena.