A controversial Philippines mayor who gained notoriety for parading people arrested on drug offenses was shot and killed by a sniper at a flag-raising ceremony Tanauan City Hall Monday morning.

Tanauan City Mayor Antonio Halili was killed by a single shot to the chest from an unknown assailant, Police Superintendent Renato Mercado told CNN, in a hit captured on video which showed scenes of panic seconds after the shot was fired.

In the video, Halili is seen standing in a line with government employees as the flag is raised and those in attendance sing the national anthem.

As the camera strays to film another group, a single shot rings out, followed by screams and a woman's voice, saying "oh my God" in English. While the victim is not seen on camera after the shot is fired, the content of the video could be upsetting to some viewers.

The mayor's security returned fire, according to state media Philippines News Agency (PNA), causing panic as government officials and staff ran for cover.

Gerry Laresma, the government employee who shot the video, told PNA it wasn't clear where the shot had originated. He said Halili had received death threats because of his strong anti-crime push.

Provincial Chief Superintendent Edward E. Caranza told PNA that the bullet was fired from a distance, most likely using a 5.56 or 7.62 caliber high-powered rifle.

Halili was declared dead at the Reyes Memorial Hospital in the city less that an hour after the shot was fired around 8 a.m. Monday (8 p.m. Sunday ET), attending physician Alexander Carandang said.

Philippine National Police Chief Director General Oscar Albayalde said that a regional special task group had been convened to investigate the killing, according to CNN affiliate CNN Philippines, and that the suspect parades were being considered as a motive.

Presidential spokesman Harry Roque condemned the killing, saying that Halili was an ally of Duterte, and that justice would be served, CNN Philippines reported.

The 'Duterte of Batangas'

Those paraded had confessed to drug offenses but had not been formally charged, Mayor Halili told CNN in an interview in 2016.

Halili started the contentious policy in 2014 with the help of his 70-strong "anti-crime group," government officials who dressed in all black and patrolled the streets, some armed with their own guns.

He came to prominence in a zero-tolerance climate for drug offenses in the country, led by President Rodrigo Duterte's infamous war on drugs, which has seen thousands of suspected drug users and dealers gunned down by police and vigilantes.

Halili identified strongly with the controversial leader -- "They call me the 'Duterte of Batangas,'" he told CNN in 2016, referring to the province in which Tanauan is located -- and said he was a proud supporter of Duterte and his controversial policies.

However, even before Duterte came to power Halili had made a name for himself with the controversial perp walks. (CNN)

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