"We have completed seven cases, including the ACF (French charity Action Against Hunger) case, and we have asked for a date to hand over the report to the president," Nissanka Udalagama said.
"I can't discuss our findings because it is up to the president to decide," he added, saying his panel would ask the president to establish a more permanent body to keep up investigations.
Thirteen men and four women who worked on water sanitation and farm projects for the ACF were found shot dead in August 2006 in the northeast of the island while troops and Tamil Tiger rebels were locked in combat.
Nordic peace monitors at the time blamed the killings -- the worst attack on aid workers since the bombing of the UN headquarters in Baghdad in August 2003 -- on government forces.
The government has denied any role in the massacre.
Udalagama's investigation has been controversial from the start, with rights activists dismissing it as a government cover-up.
Colombo did appoint 11 senior foreign diplomats and dignitaries to supervise the probe, but they eventually pulled out in April 2008 saying that the investigations did not meet minimum international standards.
Amnesty International repeated calls for the findings to be made public.
"Families of the victims and survivors need answers," said Yolanda Foster, the group's Sri Lanka expert.
"These people still have not received any justice from the Sri Lankan government... It proves a real need for an international, independent mechanism to investigate the allegations of war crimes and grave human rights violations committed by both sides."
Sri Lanka continues to come under pressure over its rights record, with the UN reporting the deaths of thousands of civilians in a government offensive that led to the defeat of the Tamil Tigers last month and calling for a war crimes probe.
The Sri Lankan president has rejected the demands.