Anny Paparoussou says Savvas Xiros, who is serving five life terms in a maximum-security Athens prison, is severely disabled.
Xiros was badly injured when a bomb he was trying to plant exploded prematurely in 2002 in Athens. He was arrested and his interrogation led to the quick unravelling of the previously elusive group that killed 23 Western diplomats and Greeks between 1975 and 2000.
Two of Xiros' brothers were among the group's members.
Recent legislation designed to ease overcrowding in Greek prisons has made it quicker to release convicts on health and other grounds.
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