Former Guatemalan dictator Efraín Ríos Montt is set to face a retrial on Monday for genocide after he was found guilty in May 2013 of that charge and of crimes against humanity — only to have a court annul his 80-year prison sentence due to procedural errors during the earlier trial.

Ríos Montt, 88, arrived Monday at Tribunal Tower in Guatemala City in an ambulance and under tight security. Last week his lawyers had argued that he is too sick to face another trial.

"The health condition of Gen. Ríos (Montt) has been deteriorating during the past year, and doctors are watching him very closely to see if he's in good enough shape to attend on Monday," Luis Rosales, a lawyer for Ríos Montt, told Agence France-Press.

José Mauricio Rodríguez, Ríos Montt’s former intelligence chief who was acquitted of the two charges in the 2013 trial, was also set to stand trial Monday.

The 2013 ruling against Ríos Montt was historic: the first time a former head of state had been prosecuted in his native country for genocide. The former army general, who ruled from 1982 to 1983, and Rodríguez were charged with ordering 15 massacres that left 1,771 Maya Ixil Indians dead in northern Guatemala. Prosecutors say it was part a scorched-earth campaign against left-wing groups and those seen as sympathetic to them.

But the country’s Constitutional Court struck down the conviction on procedural grounds. And the trailblazing attorney general who directed the genocide case, Claudia Paz y Paz, was forced out of office prematurely through legal maneuvering by opponents and a re-election process that came under fire from human rights groups.

In October, the Constitutional Court directed a lower court to reconsider its prior ruling that the country's amnesty law did not bar Ríos Montt’s prosecution. And some experts on Guatemalan politics fear that this directive may allow the appeals court to apply a 1986 amnesty law in Ríos Montt's case.

An estimated 200,000 people died during Guatemala’s civil war, from 1960 to 1996, according to the United Nations. More than 90 percent of human rights violations reported during the civil war took place between 1978 and 1984, the U.N said.

The human rights groups preparing for the retrial say that there is “convincing” proof of Ríos Montt’s role in genocide and crimes against humanity in Guatemala in the early 1980s. Juan Francisco Soto, director of the Center for Legal Action for Human Rights, said prosecutors will present 800 pieces of evidence against Ríos Montt, including military plans and testimony from 120 survivors of the attacks.

“If it was proved once, genocide will be proved again — the evidence is convincing,” Soto said. “We hope that with the repeated debate the Guatemalan justice system will show that it is capable of judging these grave crimes against humanity, and that justice will be served to the victims after more than 33 years."

With wire services