Mr Wickramatunga was shot last Thursday by unidentified gunmen
The Sri Lankan government has accused the opposition of trying to gain political advantage from last week's murder of a prominent newspaper editor.
Engineering Services Minister Rajitha Senaratne said he did not know who had killed Lasantha Wickramatunga but it was the opposition that had benefited.
The Sunday Leader editor was one of the government's leading critics. He was shot in the head by unknown killers.
A piece by him published by his paper after his death blames the government.
The editorial, entitled And Then They Came For Me, in which Mr Wickramatunga predicted his own murder, says: "When finally I am killed, it will be the government that kills me."
Ministers have not reacted to the article itself but they have strenuously denied any involvement in the murder and accused the opposition of "trying to make political capital out of a dreadful incident".
"I can't say whether it was Tamil Tiger rebels or anyone else who else carried out this assassination," Mr Senaratne said.
"But who gained from this? Who got the advantage?" he asked.
Correspondents say that the government has long maintained that a national and international conspiracy is taking place to tarnish Sri Lanka's name and Mr Wickramatunga's death is connected to this.
It argues that recent high-profile attacks on the media, including the ransacking of the country's largest independent television station, were all carried out to divert attention from military successes, including the capture of Kilinochchi - the administrative centre of the Tamil Tigers - and the strategically important Elephant Pass.
The editor's last comments contain damning indictments of President Mahinda Rajapaksa - who, he says, has been a friend of his for more than a quarter of a century - and the Sri Lankan government.
"Sadly, for all the dreams you had for our country in your younger days, in just three years you have reduced it to rubble," he tells the president.
"In the name of patriotism you have trampled on human rights, nurtured unbridled corruption and squandered public money like no other president before you.
"Indeed, your conduct has been like a small child suddenly let loose in a toy shop. That analogy is perhaps inapt because no child could have caused so much blood to be spilled on this land as you have, or trampled on the rights of its citizens as you do.
"Although you are now so drunk with power that you cannot see it, you will come to regret your sons having so rich an inheritance of blood. It can only bring tragedy. As for me, it is with a clear conscience that I go to meet my Maker. I wish, when your time finally comes, you could do the same. I wish."
In another passage, Mr Wickramatunga tells the president that he will "have no choice but to protect my killers" - and ensure that whoever is responsible is never convicted.