The magistrate in Matale instructed the Criminal Investigations Department (CID) to submit a comprehensive report to the court by the end of this month, Xinhua reported.
The CID was also ordered to record statements of 13 petitioners who claimed that their relatives were believed to have been buried at the site.
Sunil Watagala, the lawyer appearing on behalf of the petitioners, said the magistrate also ordered a DNA test on the skeletal remains found in Matale.
Sri Lankan President Mahinda Rajapaksa last month decided to appoint a special commission to investigate the mass grave.
The investigation by the commission will be in addition to the probe carried out by police.
Over 150 skeletal remains have been unearthed from the mass grave.
Forensics have determined that the remains were of people killed sometime in the late 1980s and the area has now been marked as a crime scene.
At least 10 skeletal remains were first found from the site in November last year by construction workers when land near a hospital was dug up to construct a new building.
Following police investigation, excavation began to look for skeletal remains at the site, and more human bones were found.
A Marxist political party, the JVP, has demanded that the government carry out an investigation on the mass grave following fears that the remains may be that of JVP members or supporters killed during insurgency in 1987-89.
--IANS (Posted on 10-05-2013)