Arias, founder and director of the local radio station Fresno Estéreo, was killed during the evening when an assassin burst into his home in the Tolima Department township of Fresno and shot him three times in the head.
After shooting Arias, the gunman fled on a motorcycle driven by a man waiting outside, said José Parra, an investigator at the Tolima Department prosecutor's office.
Parra said no arrests have been made, and that the reasons for Arias' assassination remain unclear. Parra reported that the region is crawling with fighters from Colombia's two main leftist guerrilla groups and a rival right-wing paramilitary army.
Before moving to Fresno earlier in the year, Arias founded and directed several other radio stations that, along with Fresno Estéreo, broadcast popular music and nonpolitical community programs, said his brother, Eduardo Arias.
Eduardo Arias told CPJ that his brother operated the radio station from his home and had never received death threats.
There had been no progress in the investigation by year's end, Parra said.