President Rodrigo Duterte ordered on Monday the Philippine National Police ( PNP) to allow the National Bureau of Investigation (NBI) to take over the investigation on the killing of Misamis Occidental Mayor David Navarro while under police custody.

In an interview with reporters, Duterte raised the possibility that the policemen killed the mayor.

"What did the PNP do? They might have killed him," Duterte said, noting that Navarro was under the custody of the policemen when supposedly shot to death by unknown assailants last Friday while inside a van that would bring him to the Cebu City Prosecutor's Office.

Duterte said he wants the NBI to conduct the investigation.

"And to make it really fair, I'd like to order the police to terminate their investigations and hand it to the NBI whatever documents and all proof or evidence that they have in their hands," he said.

Navarro was reportedly in the list of alleged "narco-politicians" of Duterte.

Duterte said the slain mayor could have been included in his initial narco-list.

But Duterte said he was not sure if the mayor's name was removed from the list later on as he admitted that Navarro was his supporter.

"He supported me during the last election," he said. Celerina Monte/DMS