Four armed assailants wearing hoods burst into the home of Cárdenas, a retired journalist who lived in the western Colombian city of Buenaventura, killing him, his son, and his brother, police said.
Cárdenas was watching an evening soccer match on television when the attackers broke into the house and opened fire, said Col. Luis Alberto Ramírez of the Buenaventura Police.
Cárdenas, 51, died from gunshot wounds to his head and chest. His son and brother died two days later.
It was initially reported that Cárdenas' teenage nephew was killed in the attack. However, Colonel Ramírez said that the nephew was stabbed to death last year, and that the November 14 attack may have been related to his slaying.
Cárdenas had worked as a news announcer with radio Carcajal Stéreo in Buenaventura and as a local reporter for several newspapers, including El Tiempo and El Espectador, two of Colombia's most prominent national publications. In the past, journalists from both papers have been targeted by left-wing guerrillas and right-wing paramilitaries, as have provincial broadcast journalists all over the country.
During the last year, Cárdenas worked as a press officer at the local fire department.
At year's end, Colonel Ramírez said the investigation had turned up nothing new. Though no one had been captured, he still believed that Cárdenas was killed for personal reasons. The prosecutor handling the case in Buenaventura, Balmer Restrepo, refused to discuss the case over the phone.