PANIQUI - Relatives of a woman and her son shot dead by an off-duty policeman in the Philippines called for justice at their wake on Tuesday amid public outrage over an incident that went viral on social media after it was caught on camera.

Sonia Gregorio, 52, and 25-year-old son Frank Gregorio, were shot in the head on Sunday after a row over noise, triggering accusations from activists that President Rodrigo Duterte's war on drugs had created a culture of police impunity.

"I lost a mother who was the most loving mother to us. I lost a brother who was also a very loving and caring brother. It's very hard for us," said Tasha Delos Santos.

"I hope our family gets justice."

Duterte on Monday condemned the Tarlac shooting and said he only defends police who do their duty, warning "there will be a hell to pay" for rogue officers.

In a video recorded on a family member's mobile phone, policeman Jonel Nuezca was seen engaging in a heated argument with the Gregorios over the use of a homemade cannon in Tarlac province, north of Manila. The devices, which make a booming sound, are typically used to celebrate New Year.

When Sonya wrapped her arms around her son as the row intensified, Nuezca shot her in the head before doing the same to Frank. Before fleeing, Nuezca shot Sonya Gregorio again.

Nuezca surrendered to police that night and faces two counts of murder. The government has promised a thorough investigation.

"They weren't criminals, they were the nicest family here," said neighbor Gonyong Liwanag.

Critics and rights groups say Duterte's talk of killing criminals and promises to protect law enforcement have emboldened police to commit and cover up murder. Police reject that.

Government data show that 5,942 suspected drug dealers have been killed by police since 2016. Rights group say that number is an understatement and accuse police of summarily executing users and pushers. Police say those killed had resisted arrest.

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