"The anger is being sustained by the government’s flagrant obstruction of the investigation," RSF said in a statement. "Lasantha Wickrematunge’s name and memory will not disappear and, in that sense, those who were behind his murder made a mistake."
RSF asked candidates at the January 26 presidential elections to pledge to probe the editor's murder and other serious press freedom violations in recent years.
The government of President Mahinda Rajapakse has denied involvement in the killing although his newspaper has said the administration was responsible.
The New York-based Committee to Protect Journalists (CPJ) also used the first anniversary of the death of Wickrematunge to draw attention to dozens of killings and attacks against journalists under Rajapakse's rule.
There is no official censorship in Sri Lanka, but many mainstream media organisations censor themselves for fear of reprisals from the authorities.
Many defence columnists stopped writing during the height of fighting between troops and Tamil Tigers earlier this year.In September, a Tamil editor was jailed for 20 years of hard labour on charges of supporting terrorism.
Government figures show nine journalists have been killed and another 27 assaulted in the past three years while activists say over a dozen journalists have been killed.