(CNN) -- A team of forensic experts who testified in a high-profile trial that saw former members of the Guatemalan army convicted of crimes against humanity have received death threats for their participation, Amnesty International said Friday.
The human rights organization called for Guatemala to find and punish those making the threats.
Four staff members from the Guatemalan Forensic Anthropology Foundation testified in the trial of the four former soldiers about their role in the massacre of 250 people in 1982 during the country's civil war. They were convicted this month in 201 of the killings and sentenced to more than 6,000 years in prison each.
The founder of the forensics foundation, Freddy Peccerelli, received a death threat hand-written in red ink on August 8, Amnesty said.
"Sons of a bitch. You will pay us slowly, for each of the 6050 years that our people are going to suffer because of you, now we won't simply watch you we will leave you battered like the rest," the note said, according to Amnesty.
The note also said in part, "when you least expect it you will die. Revolutionaries your DNA will be of no use. Your families will pay, you will follow suit."
The convictions were considered historic and were hailed by family members and activists. The trial was one of Guatemala's first against dictatorship-era ex-soldiers.
The massacre happened at the village of Dos Erres, located in the northern Guatemalan province of Peten. It was part of a civil war that claimed thousands of lives. Activists hope that the recent conviction will set a precedent for future cases against former soldiers.
The note that Peccerelli received also mentioned three colleagues who also testified at the trial. The four had testified about their work to exhume and analyze the victims of the massacre, according to Amnesty.
"It is unacceptable for expert witnesses to be intimidated like this, and Guatemalan authorities must order an independent, thorough and impartial investigation into these threats and bring those responsible to justice," said Sebastian Elgueta, Amnesty International's Central America researcher.
"Guatemalans have waited nearly three decades for justice in the case of the Dos Erres massacre and hundreds of other grave human rights violations, and the failure to stop such death threats would cast a pall over the judicial process," he added.