A long-awaited report from the United Nations human rights office on Wednesday laid bare horrific wartime atrocities committed by both the army and the separatist Tamil Tiger rebels in the bitter 37-year war.
It came as President Maithripala Sirisena's new government vowed to punish war criminals, with a promise to set up a truth commission and a reparations office to help heal the wounds left by the conflict.
"That (denial) was the biggest mistake Sri Lanka made," government spokesman Rajitha Senaratne said.
In the northern Tamil capital of Jaffna, roads and other war-damaged infrastructure have been repaired and where the military was once a constant presence in people's lives, surveillance is a thing of the past.
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Yet thousands are still living in refugee camps six years after the war ended in May 2009, and bombed-out houses and bullet hole-riddled buildings still scar the streets.
They have the support of the UN, which has called on Colombo to bring in international judges and prosecutors to assist in investigations as the only concrete way to achieve accountability.
But Sirisena, who favours a domestic inquiry, has stayed quiet on the issue.
"People in Jaffna are not aware of what is going on in Geneva, but what they are hoping for is justice," said local Tamil politician Suresh Premachandran.
Sri Lanka became an international pariah after repeatedly resisting calls for a credible probe into the horrendous crimes allegedly committed by government forces during and after the war.
British Prime Minister David Cameron, who attended the summit, used his visit to heavily criticise Rajapakse after becoming the first foreign leader to travel to battle-scarred Jaffna since Sri Lanka, a former British colony, gained independence in 1948.
The Tamil Tigers suffered a bitter defeat in a no-holds barred military campaign that also killed thousands of troops.
The UN says 40,000 Tamil civilians died at the hands of government forces in the final months of the conflict as the army moved to crush the guerillas.