An inquiry was launched on Thursday into the 2012 prison riot in Welikada which led to the deaths of 27 inmates, mainly Sinhalese, at the hands of Sri Lankan security forces, AFP reported.
Eye witnesses said the officers executed many of the inmates in cold blood.
The launch comes just days before the anniversary of the worse massacre at the prison on 25th July 1983 when 54 Tamil detainees murdered by Sinhala inmates.
Over three decades later no inquiry has been held and no one has been brought to justice.
Prison riots in 1997 and 2000 also saw Sinhala inmates murdering Tamil inmates.
Fearing a repeat, in 2012 as the riots took hold, more than 180 Tamil political prisoners were reportedly moved from Magazine prison in Welikada to another jail for their own safety.