Members of the Greek radical group November 17 have appeared in court to appeal against convictions for more than 2,500 crimes.
The hearing offered Giotopoulos a chance to make a stand
Fifteen members of the group were found guilty in 2003 for a 25-year campaign of murder and violence.
The group's head, who was sentenced to 21 life terms, described his conviction as "ridiculous and unreasonable".
A five-member panel will consider the appeals, which are expected to last several months.
The hearings are being held at Athens' maximum security Korydallos prison, where 13 of those convicted are being held.
Alexandros Giotopoulos, a mathematics professor and leader of the radical leftist group, proclaimed his innocence during a break in proceedings.
"I was [sentenced] for politically motivated reasons and because of foreign blackmail," he said.
"If the court is even slightly fair it has only one option and that is to acquit me."
Athens Mayor Dora Bakoyanni, whose conservative MP husband was killed by the group in 1989, was in court to hear the opening exchanges.
"We have every faith in the Greek justice system," she said, insisting that the convictions would not be overturned.
"What we expect is to find out some more things about this terrible, terrible case."
The original three-judge panel spent nine months hearing evidence related to some 2,500 crimes including murder and robbery.
Brigadier Saunders was the last person killed by the group
November 17 took its name from the date of the crushing of a student uprising in 1973 during military rule in Greece which lasted from 1967 to 1974.
The radical leftists' attacks were aimed at overthrowing capitalism and attacked US targets because of Washington's support for the junta.
They are believed to have killed four US officials, two Turkish diplomats and a UK military attache in addition to their Greek victims.
A 20-year statute of limitations in Greek law means that group members will not be sentenced for the first four killings blamed on November 17 - including that of CIA station chief Richard Welch, whose 1975 assassination marked the group's first appearance.
Brigadier Stephen Saunders, who was shot dead as he drove to work in Athens in June 2000, was the last person killed by November 17.