A judge has announced that the more than 150 human skulls and bones recovered from a mass grave in Sri Lanka were buried there about 25 years ago, strengthening suspicion that they belonged to suspected Marxist rebels.

Magistrate Chathurika de Silva told a court in the central town of Matale on Wednesday that tests carried out by archaeological and judicial medical officers show the skeletal remains found on the premises of a government hospital dated to between 1987 and 1990. During that period, thousands of men and women suspected of having ties to the rebels disappeared after being arrested by security forces.

Mr. Justice De Silva did not explain the cause of death but declared the mass grave a crime scene. The military could not be contacted immediately for comment.

Workers found the human remains during construction on the hospital land last December. The bodies had been buried in neat rows, stacked five or six deep, totalling 154.

Claims were made initially that the bodies belonged to those killed in an epidemic in the 1940s or a mudslip.

However, hospital authorities did not have any records of bodies buried on the premises.

The Marxist group People’s Liberation Front, which led two uprisings — first in 1971 and from 1987 to 1989 — claimed the bodies may belong to comrades killed by security forces.

“The state’s army and paramilitaries carried out large scale killings at that time and we ask the government to do a full investigation,” said Anura Dissanayake, a lawmaker from a political party with ties to the former rebels.

The Marxists were mostly rural Sinhalese, the majority ethnic community. They complained of economic disparities and said that rural people were denied equal opportunities. — AP