In the first case of its kind since the end of the communist era in Romania, an appeals court in Bucharest has upheld a jail sentence against a prison commander convicted of crimes against humanity for the death of 12 political prisoners more than 50 years ago.

Alexandru Visinescu, 90, was sentenced to 20 years in jail last last July after being found guilty of running “a regime of extermination” at the jail outside the small town of Râmnicu Sărat, 90 miles east of the capital, from 1956 to 1963.

The prisoners, members of Romania’s pre-war intellectual, political, and military elite, were held in solitary confinement in unheated cells, subjected to regular beatings, severely underfed, and denied access to medical treatment.

At least 14 of the 138 inmates who were detained at Râmnicu Sărat during the seven years Visinescu was in charge at the jail died, prosecutors said, while many more were permanently disfigured or traumatised.

The first prison commander to face trial since Romania’s former dictator Nicolae Ceauşescu was executed in 1989, Visinescu, who was not in court to hear the verdict on Wednesday, has shown little remorse, insisting he was merely following orders and blaming the Stalinist regime of Ceausescu’s predecessor, Gheorghe Gheroghe-Dej.

Asked six times at his appeal hearing in the high court of cassation last month why prisoners had died under his command, he replied just once, suggesting they had probably died of old age, before breaking down and pleading: “Let me die.”

Survivors of his regime have described being banned from sitting on their beds except at nighttime, or from approaching cell walls in case they used morse code to communicate with each other.

The widow of one detainee, General Ion Eremia, who spent 14 years in the prison, said her husband was forced to spend hours standing with his bare feet in a bucket of freezing water and left the jail weighing barely 30 kilos.

The ruling marks a significant moment in Romania’s efforts to bring to justice communist-era figures accused of wrongdoing. While a handful of top officials were convicted of genocide in the 1990s, most of the charges were later reduced and many of those found guilty were released on health grounds.

According to the Institute for Investigation of Communist Crimes and Memory of Romanian Exile (IICCMRE), which initiated the case against Visinescu, up to 2 million Romanians were killed, unjustly imprisoned, deported or relocated during nearly half a century of communist repression.

Historians have said more than 600,000 dissidents – including landowners, politicians, priests, lawyers, doctors, writers, teachers and students – were jailed for crimes against the state from the late 1940s onwards. As many as 100,000 are thought to have died in prisons like Râmnicu Sărat.

The IICCMRE has said it has a list of 35 prison officials, most now aged between 80 and 100, who it says have committed crimes. It blames corruption, still widespread in Romania, for the fact that so far only Visinescu – who was living openly in central Bucharest on a special military pension – has been sentenced.

Andrei Muraru, the organisation’s former head, said he was gratified by Wednesday’s ruling. “It is a historic sentence because, starting from this moment, any crimes committed in the communist era can be condemned,” Muraru told the Associated Press.

The IICCMRE’s current chief, Radu Preda, described Visinescu’s trial last year as “particularly important” because “for the first time, an instrument of communist terror will face justice. Without hyperbole, this amounts to a Romanian Nuremberg,” he said.