“The distance from the position was extraordinary. It could not be done by an ordinary person. His skill can be compared to a trained sniper,” he said

Phone video of the shooting went viral on social media. It showed a single shot ringing out as the anthem played outside city hall, then screaming and pandemonium.

The bullet hit a mobile phone in Halili’s coat pocket then pierced his chest, police said.

Police were scouring a nearby elevated grassy area, where the gunman may have fired the shot.

Halili became controversial two years ago when he ordered drug suspects to be paraded in public in Tanauan, a small city about 70 kilometres (43 miles) south of Manila, in a campaign that was dubbed “walks of shame”.

The suspects were forced to wear cardboard signs that read “I’m a pusher, don’t emulate me” in a campaign that alarmed human rights officials.

But in 2017, Halili’s name surfaced on a “narco-list” presented by President Rodrigo Duterte, of officials allegedly linked to narcotics.

Halili was stripped of control of the police following the publication of the list, but he denied any ties to drugs.

He said at the time that he would resign and would be willing to be publicly paraded as a drug suspect if police could come up with evidence to support the allegation.

Philippine National Police chief Oscar Albayalde said investigators would try to determine if the killing was connected to Halili’s anti-drug campaign.

Halili’s unusual campaign drew attention at a time of growing alarm over the rising number of killings of drug suspects under Duterte.

Since Duterte took office in 2016, more than 4,200 drug suspects had been killed in clashes with police, alarming human rights groups, Western governments and UN rights watchdogs.

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In an interview with Reuters in August 2016 - the second month of the crackdown - Halili said he backed Duterte’s campaign but believed drug kingpins should be the main targets, otherwise thousands of people would be killed.

He expressed concern over the way police conducted the war on drugs and the reliability of their intelligence, and that he might be accused of colluding with narcotics gangs.

“No one is safe – mayors, governors, congressmen – just a false intelligence report by the police can end up with any of them being destroyed,” he said in the interview.

“I have a feeling they (police) are going after the small fry to frighten the people,” he said.

Human rights groups have reported much higher death tolls, although Duterte and his officials have questioned the accuracy of those reports.

They said the suspects died because they opened fire and sparked gunbattles with authorities although human rights groups have accused police of extrajudicial killings.

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Though the Philippines sees occasional slayings of local politicians, the brazen nature of the killing and links to Duterte’s drug war drew immediate outrage.

“This is clearly another case of EJK (extra-judicial killing) resulting from the so-called drug war launched by the government,” opposition leader Senator Francis Pangilinan said in a statement.

“It is this Philippine image of a ‘wild, wild west’ that has also dampened the desire of both foreign and local investors.”

Three other mayors on the “narco-list” have been shot dead, one of them while being held inside a jail cell.

Mercado, the Tanauan police chief, said that the killing may be linked to the illegal drugs allegations.

Duterte’s spokesman Harry Roque condemned the crime and praised Halili as the mayor of “one of the most progressive towns” in his province.

Associated Press, Reuters, Agence France-Presse