Mr. delos Santos, a high school student, was among 96 people killed in the Manila area last week in what the police called a “one-time, big-time” crackdown on drug dealers and addicts in the capital and several sprawling suburbs. It was the bloodiest week of the antidrug campaign that Mr. Duterte started after taking office last summer, promising to rid the country of corruption and crime.
The police said Mr. delos Santos had been carrying a handgun when they encountered him on Aug. 16, and that they had shot him in self-defense, after he “fought it out” with them. The police have a term for that, “nanlaban,” which has become associated in the Philippines with police killings.
But since the teenager’s death, surveillance camera footage has emerged of police officers forcefully leading him away — contradicting accounts of a spontaneous shootout. Witnesses said they had seen officers dragging Mr. delos Santos to a cul-de-sac near a community basketball court, handing him a gun and telling him to run — only to shoot him as he turned to do so.
An autopsy found that Mr. delos Santos had been shot at least twice in the head, at close range. At his wake, his father told reporters that a gun had been found in the boy’s left hand, though he was right-handed. The teenager had wanted to be a police officer, the father added.
The police have killed more than 3,500 people since the beginning of Mr. Duterte’s crackdown, according to their own count, and they note that the vast majority had resisted arrest. While many Filipinos have expressed doubts about that point, rarely if ever have there been surveillance camera images contradicting a police account of a shooting, as in Mr. delos Santos’s case.
The outcry in this case has Mr. Duterte and his allies scrambling to contain the fallout. Some of the president’s supporters in the Senate crossed party lines to vote in favor of an investigation into the Santos killing. A Senate hearing on the case will be held on Thursday.
“I agree that there should be an investigation,” Mr. Duterte said on Monday. “If there is liability, they will go to jail.”
The president added that he had ordered that the officers involved in the teenager’s death be taken into custody — a reversal from his frequent promise to pardon officers who kill suspects without provocation.
The American ambassador to the Philippines, Sung Kim, offered his condolences to Mr. Santos’s family and said he hoped that the “investigations lead to full accountability,” a rare foray by an American diplomat into a volatile domestic issue.
Mr. Santiago, the rights advocate, said the surveillance footage in Mr. Santos’s case proved what critics had long argued: that extrajudicial killings in the Philippines are routinely passed off as “nanlaban” shootouts. Mr. Duterte should order a far broader investigation, he added.
“His sincerity can only be determined in his resolve to make perpetrators of crimes accountable, including those involved in his anti-illegal-drugs campaign,” Mr. Santiago said.
Senator Risa Hontiveros said she was saddened that it had taken a boy’s death for the country to realize “how corrupt and abusive President Duterte’s drug war really is.”
While Ms. Hontiveros noted that it was too early to say if the episode would turn the tide against police killings, she said she was hopeful that the public would demand accountability from Mr. Duterte.
Reflecting growing indignation, thousands of rights activists and others braved strong rains on Monday to show their support for Mr. Santos’s family.
Ramon C. Casiple, a political analyst at the Institute for Political and Electoral Reform, said that the accounts from witnesses and the forensic evidence in Mr. Santos’s death had fueled outrage.
“Duterte knows this can be transformed into a political issue against his administration,” Mr. Casiple said. “I think he wants to defuse the situation before it becomes a real threat to his presidency.”
Mr. Duterte has shown himself to be very resilient, however, and his down-to-earth appeal, rooted in a leftist anti-establishment streak, should serve him well, analysts said.
That Filipinos welcomed the president’s promise to punish Mr. Santos’s killers is too little, too late, Ms. Hontiveros said.
“This cannot make us forget his other words that have inspired, abetted and condoned the senseless killings in the name of the war on drugs,” she said. “The president’s hands are stained by the blood of Kian.”
“He inspired this culture of impunity and killing,” she said of Mr. Duterte. “He reveled in the deaths of drug addicts, while at the same time turning a blind eye on the big drug lords close to him and his family.”