Suspected members of the Revolutionary Armed Forces of Colombia attacked a car carrying Jaime Lozada, a former national senator who once served as governor of the southern Colombian province of Huila, on a country road on Saturday evening, a police spokesman said on Sunday.
Lozada was killed and his son Jaime Felipe was wounded in a leg in the ambush.
The rebel army known by the Spanish initials FARC had held Jaime Felipe and his brother Juan Sebastian hostage for three years until their release in June 2004, when their father admitted paying a ransom.
A survivor of Saturday's attack, journalist Jorge Masmelas, described two blasts hitting the car followed by gunfire. He said Lozada's last words were of concern for his sons.
One possible explanation for the attack, for which the FARC has not claimed responsibility, is that Lozada still owed the guerrillas ransom money, a police spokesman said.
The rebels, a peasant militia fighting for socialist revolution since 1965 that has grown powerful thanks to cocaine money, still hold Lozada's wife, Gloria Polanco.
The rebels kidnapped Polanco and her two sons in a spectacular raid on an apartment building in the city of Neiva in July 2001. Rebels disguised as police went from door to door in the exclusive building and kidnapped an additional 12 people.
Ingrid Betancourt has been held
hostage by FARC since 2003
Polanco was elected to Congress during her captivity in 2002 and the FARC has now included her in a list of 63 politicians, police officers and soldiers they are holding hostage and say they will only release in exchange for jailed guerrillas.
Three US civilian Defence Department contractors captured in 2003 while searching for illegal drug crops are also on the list, together with former presidential candidate Ingrid Betancourt, a dual Colombian-French national.