The victim, Conrado Rodrigo, 53, father of incumbent Mayor Christopher Jones Rodrigo, had just come from a meeting also attended by his son and was walking on his way home without any bodyguard when he was shot.
Police said three men shot the elder Rodrigo, president of the towns barangay league, several times with caliber .380 and .45 pistols.
During the meeting near his residence, Rodrigo appealed to the people to support whoever won in the towns mayoral race. His son lost.
In an earlier interview with Bombo Radyo Dagupan, he said his son failed in his re-election because the townsfolk probably did not like them anymore and the smear campaign of his rivals worked.
One of the suspects in Rodrigos gunslaying, a certain Jonathan de Leon, 26, was subsequently arrested. His two accomplices are being hunted down.
Rodrigo survived an ambush in August last year after he shot it out with his attackers. He was hit in the leg and underwent an operation.
Rodrigo, who marked his birthday last May 21, was a former communist rebel. He served as San Nicolas mayor for 11 years.
During the recent campaign period, a bodyguard of Leoncio Saldivar, his sons rival, was shot dead near the public market, prompting the Commission on Elections to place the town under its control. With Cesar Ramirez and Artemio Dumlao