Police initially identified four of the fatalities as siblings Melchor and Elmer de Chavez, operators of the Sariaya Sports Complex; Marvin Abarsoza and Marlon Cabrera. The fifth remained unidentified.
Quezon provincial police director Senior Superintendent Hernando Zafra said Elmer was buying some snacks at a roadside eatery near the cockpit when three men approached from behind and shot him at close range.
Melchor, in his attempt to rescue his wounded brother, figured in a shootout with the assailants, fatally hitting three of the gunmen.
Witnesses added Melchor was later shot down by other suspects during the four-minute gunplay.
The brothers succumbed to multiple gunshot wounds while being treated at the Greg Hospital in the town.
The police immediately ruled out the killing as politically-motivated.
"The De Chavez brothers have been receiving death threats even before the election period," according to Chief Inspector Sergio Vivar, Sariaya chief of police.
The De Chavez brothers are cousins and main supporters of incumbent Sariaya mayor Connie Doromal who is seeking re-election.
Police have launched manhunt operations against the other gunmen who managed to escape during the shootout. – Arnell Ozaeta, Ed Amoroso