Right now, the Sri Lankan government's response has been to wait and see. They want to wait and see what happens with the LLRC and they want to take a bit more time.
The response has actually changed. Previously, the government refused to admit there were any civilian casualties whatsoever. In their propaganda offensive, they continued to claim that in the final stages the war was a humanitarian effort by the Sri Lankan government to rescue civilians, and that there were no civilian casualties in that effort.
Since the release of the UN panel of experts report and the Channel 4 footage, that position has been hard for them to maintain. Now they admit that there may have been some civilian casualties, but they want to wait and see. They want to wait and see what happens with the LLRC report.