July 2, 2018 1:59 AM EDT

A Philippine mayor known for parading drug suspects on “perp walks” has been shot dead in Tanauan City, Batangas province, about 40 miles south of Manila.

Mayor Antonio Halili was taking part in a weekly flag raising ceremony in front of Tanauan’s city hall Monday when he sustained what local authorities say was a sniper shot to the chest, state media Philippines News Agency reports.

Halili gained local notoriety in 2016 for implementing a “walk of shame” for drug suspects, according to local news site Rappler. But authorities later included him on a list of government officials, congressmen, and mayors, allegedly linked to the illegal drug trade. Halili was stripped of his powers to supervise local anti-drug operations in November 2017.

Police have not yet confirmed a motive for the shooting.

In a rare concession to human rights, the Philippine National Police (PNP) in June said it would end its practice of parading drug suspects on “perp-walks” before the media.

“While we did not agree with Mayor Halili’s method of dealing with crime and illegal drugs in his city, his murder is condemnable,” Human Rights Watch said it a statement. “He may have deprived many Tanauan residents of due process but that doesn’t mean he should be deprived of it too.”

Officially, police have killed more than 4,250 people in anti-drug operations since Philippine President Rodrigo Duterte took office on June 30, 2016. However an opposition senator claims more than 20,000 people may have been killed on Duterte’s watch, citing a further 16,355 homicide cases classified as deaths “under investigation” from July 1, 2016 to Sept. 30, 2017.

Read more: A New Netflix Series Tells the Story of the Philippines’ Drug War. But Its Critics Are Condemning Amo as Propaganda

Before Halili’s death, Philippine police had killed at least three other mayors with alleged links to illegal drugs. Last year, Duterte reinstated 19 police officers who participated in the murder of Leyte mayor Rolando Espinosa while he was in jail.

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Write to Joseph Hincks at joseph.hincks@time.com.

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