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MANILA (UPDATE) - A lawmaker on Tuesday called on the National Bureau of Investigation to conduct an "impartial" investigation into the death of Calbayog City Mayor Ronald Aquino, who he said was killed in an ambush and not a shootout.

"Humihingi ako ng tulong (I am asking for help). I can't get justice from the Philippine National Police, I believe so," Samar 1st District Rep. Edgar Mary Sarmiento told Teleradyo.

Sarmiento refuted the police's claim the incident was a shootout.

"Ako'y nasasaktan na pinalalabas na shootout doon po sa ground zero. Maliwanag na maliwanag na sinasabi ng mga witnesses na talagang binaril muna ang sasakyan ni mayor," he said.

(It is painful for me that they're saying it was a shootout. It is clear according to witnesses that the mayor's vehicle was shot first.)

"Doon naman sa mga nang-ambush, masakit sabihin kaya lang mga naka uniporme ito, mga miyembro pa ng PNP. Akoy nagtataka bakit naka-bonnet at saka naka M-203 pa. Talagang handang-handa."

(To those who conducted the ambush, it is painful to say but they were in uniform, they were members of the PNP. I am wondering why they were wearing bonnet and using M-203. It was all planned.)

• Calbayog City mayor namatay matapos ang 'shootout' laban sa mga pulis

Monday's supposed encounter in Barangay Lonoy, Calbayog City also led to the death of 3 others, including Aquino's close-in security detail and driver. Sarmiento also claimed 2 members from the PNP were killed in the incident.

• Calbayog City mayor's vehicle ambushed; 3 dead, 1 in critical condition - PNP

Sarmiento believes the killing was politically motivated.

"It all boils down to politics. The reason why Samar belongs to the top 12 poorest provinces of this land," he said.

In 2011, then Calbayog City Mayor Reynaldo "Ining" Uy was killed by unknown assailants while attending a fiesta celebration in Hinabangan town.

Sarmiento also dismissed allegations Aquino was involved in illicit drugs. Aquino was reportedly on his way to attend the birthday celebration of his child when his vehicle was ambushed.

"I am appealing once again to President Rodrigo Roa Duterte and this time to the Department of Justice (DOJ) Secretary Menardo Guevarra to allow the National Bureau of Investigation to investigate what happened since uniformed personnel who are supposed to be the protectors of peace and order were involved in the shooting incident," he wrote in a Facebook post.

The Eastern Visayas regional police has formed a special investigation task group to look into the mayor's slay, said information officer Police Lt. Col. Ma. Bella Rentuaya.

--With reports from Ranulfo Docdocan