Police said the victim, Jaime Quijano, was waiting for a Weena bus along the highway when motorcycle-riding men pulled over and fired at him with caliber .45 automatics.
Matalam is the hometown of the owner of the bus company, the lone transport firm which has been serving the Cotabato-Davao route for more than two decades now.
Officials of Carmen town said there has been persistent talk that Quijanos killers were cohorts of those behind the Digos bombing.
North Cotabato Gov. Emmanuel Piñol said he is ready to shell out an earnest amount for information leading to the arrest of Quijanos killers and the Digos City bombers.
Digos City Mayor Arsenio Latasa has offered a reward of P100,000, on top of a similar amount which Philippine National Police chief Director General Arturo Lomibao was willing to put up.
Police earlier said a criminal syndicate calling itself the Urban Tiger Action Group led by one Commander Tiger could be behind the blast.
Lomibao said the New Peoples Army had nothing to do with the explosion.
More than a dozen Weena buses have been bombed by suspected extortionists in the past two years. - With Edith Regalado