Unidentified gunmen on Monday fired shots at the house of one of the key eye witnesses to the 2012 shooting at Welikada prison.
The witness, Sudesh Nandimal, wa not injured in the attack. He was residing at his sister's house in Moratuwa.
Several shots were fired at the property's gate. The police were informed at 11pm last night, the Daily Mirror reported.
In July, an inquiry was launched into the Welikada incident, where 27 inmates, who were mainly Sinhalese were killed during a prison riot by security forces.
Eye witnesses said the officers executed many of the inmates in cold blood.
The launch came just days before the anniversary of the worst 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.