A judge in Sri Lanka has declared a mass grave where human skulls and bones had been removed is a crime scene.

It was announced that the 150 skulls and many bones exhumed from a mass grave were buried about 25 years ago, meaning they almost certainly belonged to suspected Marxist rebels killed at that time.

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

Marxist group, the People’s Liberation Front, which led two uprisings first in 1971 and 1987 to 1989, says that 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 military could not be contacted immediately for comment.