In a statement, the NPA Arnulfo Ortiz Command accused Mayor Benito Astorga of Daram, Samar of having committed injustices, including the killings of civilians in Barangay Birawan where he was shot dead.
Astorga, 47, was attending a benefit dance as part of Birawans fiesta celebration when five men attacked him. He sustained five gunshot wounds in the head, chest and other parts of the body.
Senior Superintendent Asdali Abah, Samar police director, said his office received the NPA statement Saturday afternoon.
Despite the NPAs admission, Abah said they would continue the investigation into Astorgas killing.
"We are determined to complete our (probe) We will consider this angle but we are very careful because anyone can make (such a statement) and fabricate such allegations," he said.
Earlier, Astorgas family asked the National Bureau of Investigation (NBI) to help the police probe the killing.
Lawyer Antonio Pagatpat, NBI regional director, said they were pursuing leads in the case, although he appealed to witnesses to help the investigators.
Pagatpat said they were giving weight to the political angle, but added that all possible motives were being looked into.
"Let us wait and see what evidence we could gather," he said.
Earlier, Camp Crame officials tagged Astorga as possibly the first victim of election-related violence for this year in the run-up to the May mid-term polls.
Astorga was the second member of his family to have been killed. In 1986, his brother Dioscoro, then the police chief of Daram town, was slain, and the case remains unsolved.
In its statement, the NPA accused Astorga of having a hand in the 2001 gunslaying of municipal election officer Willy Gudane and grabbing the land of small farmers in his town.
Astorgas family refused to comment on the rebels allegations, saying the investigation was still ongoing.