Sudesh Nandimal, secretary of the committee to protect rights of prisoners, yesterday (12) complained to Tissamaharama Police that an anonymous caller had warned him on the previous night against exposing details of the incident.
He said he was told not to give evidence and to withdraw from the case, or else, that being a betrayer, his life would be lost.
Nandimal has been summoned to the CID tomorrow to give a statement with regard to the November 2012 clash between the prisoners and the security forces that also left more than 40 injured.
President of the committee, lawyer Senaka Perera too, has received death threats over the phone on the same night.
He has lodged a complaint with Nittambuwa police.
On 10 February 2016 too, Nandimal was threatened by a group at Moratuwa which demanded him to abandon his efforts to ensure justice over the Welikada killings.
They had told him that if not, he would be sent six feet under.
Report not publicized yet
Retired judge Nimal Nambuwasm investigated the murders and handed over a report to justice minister Wijedasa Rajapakshe in the presence of prime minister Ranil Wickremesinghe in June 2015.
It is yet to be made public.
That was after Nandimal complained to the CID in March 2015 that he was an eyewitness to the killings and sought an investigation.
He filed a petition in May 2017 seeking a writ order to speed up the investigation.
Probe began four years later
CID ordered to investigate
Meanwhile, police spokesman Ruwan Gunasekara said the CID was conducting an investigation on an order by IGP Pujith Jayasundara.