He has told BBC Sandeshaya in London on the sidelines of the Commonwealth Day ceremony that if the inquiry finds anyone guilty, they will be punished in accordance with the laws of the country.
The president said however, there was no need for the UN inspectors investigating the allegations to visit the country.
We have clearly asked to place trust in the local mechanism, he said, adding that such a mechanism could be strengthened by taking views from the UN.
He ruled out the involvement of outsiders, but welcomed any suggestions.
The president said the National Security Council has been asked to report to him whether the hundreds of LTTE suspects in detention could either be prosecuted or freed.
The freed persons would be allowed enjoy the same freedom enjoyed by other citizens of the country, he added.
Mr. Sirisena said it should not be forgotten that his government had come to power just two months ago.