MANILA — The murder of Negros Oriental Gov. Roel Degamo was planned as early as December, the police said Friday.

According to Police Lt. Col. Gerard Pelare, spokesperson of Special Investigation Task Group Degamo, the suspects were recruited last year to conduct casing and surveillance "to determine the best option on how to attack the governor".

"These are highly-trained individuals who were hired to perpetrate this gruesome crime," he told ANC's "Headstart".

"In other words, this is a well-prepared attack na may mga mataas na kalibre ng firearms na ginamit to ensure they could overcome the security detail of the governor and kill the governor."

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Pelare said the task group is not singling out Negros Oriental 3rd District Rep. Arnolfo Teves Jr in the investigation. "We are looking into everyone not only Congressman Teves," he said.

This comes after one of the suspects implicated Teves in the killing.

"We have heard of this. We know of this information already from the suspects," Pelare said, adding the task group has already submitted the complaints to the Department of Justice.

"We already have substantial information of what transpired before, during and after the incident as well as those personalities named by the suspects," he added.

The task group is looking into personal grudge and intense political rivalry as possible motives for the killing.

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Negros Oriental is 1 of 2 provinces on Negros island, which is the center of the nation's sugar industry and home to some of the country's wealthiest landowners as well as some of its poorest farm workers.

Degamo, 56, was the latest politician to be shot in the Philippines since last year's general election.

The Supreme Court declared him last month the rightful winner of the contest for the Negros Oriental governorship following a recount that unseated his rival, who had previously been proclaimed victor.

One suspect was killed in a shoot-out while 4 others have been arrested.

The police are still on the lookout for 12 more people involved in the killing.

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— With a report from Agence France-Presse