Dr. Kasipillai Manoharan, father of one of the students, has told BBC Tamil Service that they did not expect that justice would be given from the local investigation.
He said the Sri Lankan government probe was still at the preliminary level, and that they were losing hopes for justice.
Noting that the Nadaraja Raviraj murder case was heard before an all Sinhalese-jury and the accused acquitted, he said any government would grant them a similar ruling only.
He said he would not abandon his attempts to ensure justice for his son.
Kasipillai said they were oppressed in Sri Lanka because they were Tamils, and that they were pressing on with the hope of respite for their community at least in the future.
Most of the families of the six slain students have fled the country due to death threats they have received.
Seven years after their murder on 02 January 2006, 13 STF men, including an ASP, were arrested on suspicion, and were released on bail.