MANILA- Police on Thursday told a Senate inquiry that a high school student killed last week by anti-drugs officers had been involved in narcotics, but officers only learned of that the day after they shot him dead.

The death of 17-year-old Kian Loyd delos Santos, one of thousands of Filipinos killed under the country's fierce war on drugs, has stirred unprecedented public attention on to what activists say are executions and systematic abuses by police backed steadfastly by President Rodrigo Duterte.

Roberto Fajardo, the Northern Police District chief relieved of his duty after the slay, told the hearing there was no specific target in the Aug. 16 operation in Caloocan City, but that police could confirm Delos Santos was involved in drugs.

Asked if those drug links were known after the killing, Fajardo said: "Yes. We have to check the background. We checked after."

He said a drug suspect arrested the following day confirmed Delos Santos was dealing drugs.

Chito Bersaluna, the former Caloocan police chief also removed after the killing, said Delos Santos could be tied to the drug trade by a recovered cellphone and "based on what came out on social media" after his killing.

The police admissions are seen to add to the growing scrutiny on law enforcers behind a crackdown that Duterte on Wednesday said would not stop. He said there was no justification for the student's killing, and police responsible would face justice.

• READ: Duterte: Kian's death 'bad,' but drug war to continue

Earlier police reports said Delos Santos was killed because he was carrying drugs and shot at plain-clothes officers who tried to arrest him. His family has dismissed that as a lie.

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Security camera footage showed two policemen dragging a man matching the description of Delos Santos to an alley where he was later found dead with a gun in his left hand.

Three police officers accused of involvement in the killing said little during the inquiry. One refused to speak, while the other two said the individual on the CCTV camera was their "asset", and was not Delos Santos.

Critics accused Duterte of turning a blind eye to police abuses, with an unquestioning acceptance of an official police line that typically says those killed were all drug dealers who had violently resisted arrest.

Filipinos remain largely supportive of a campaign the government says has made the streets safer.

The Delos Santos case is being closely watched by the public due to inconsistencies in police accounts and statements by relatives and witnesses who say he was brutally murdered and had no involvement in illicit activities.

The Public Attorney's Office said its autopsy showed he was shot twice in the head and once in the back, while police said their forensics showed there were only two gunshot wounds. Both indicated he was kneeling when he was killed.

Senators asked police pathologist Jocelyn Cruz to provide photographs of the autopsy, but Cruz said police did not have them.

Asked if the autopsy results indicated the student was executed, national police chief Ronald dela Rosa said: "If you shoot someone kneeling, you are a criminal, murderer. You are not a law enforcer."

• READ: PNP, PAO agree on autopsy: Kian already down when shot

Delos Santos was among more than 90 people killed last week in three nights of intensified raids called "One Time, Big Time", taking the bloody crackdown to a new level.

After 32 were killed in Bulacan province in a single night, Duterte said: "Let's kill another 32 every day".

Activists and political opponents say that kind of rhetoric is to blame for what they say is a culture of impunity among police who are repeatedly promised blanket protection from Duterte.

He took a softer tone on Wednesday, however, telling police they should do everything possible to arrest suspects and kill only when necessary. He said he would not protect police who killed illegally, and abuses "cannot be done".

• READ: Duterte: If guilty of 'rubout', cops behind Kian’s killing must go to jail