It was the latest in a series of attacks on Sri Lankan journalists, many of them fatal, since the government launched a military campaign to defeat the Tamil Tiger separatist movement after a ceasefire unravelled in 2006.
Human rights groups argue that the government has failed to investigate many of the attacks despite repeated requests. Wickrematunge was critical of the government, while Rivira is an independent publication viewed as taking a relatively neutral position on the conflict.
In a recent parliamentary session, Dinesh Gunawardena, Sri Lanka's urban development minister, said at least nine journalists had been killed and 27 attacked since 2006.
The Sri Lankan government announced last week that it would create a special police team to investigate attacks on the media.