Every fortnight six-year-old Sahar Mohammadi left home in the southern Iranian city of Kermanshah with her grandmother and made a 600-mile round trip to Evin prison in north Tehran.

There, her mother, Sussan Amiri, was being held with fellow activists, mainly leftwingers, who later became victims of an unpublicised massacre of thousands of political prisoners in the 1980s. "We were going to Evin in the hope they would let us in," said Mohammadi, now 33. "But she was not allowed visitors and I didn't get to see my mother at the end."

When Amiri was executed after refusing to repent, the family was told she had been taken to Khavaran cemetery near Tehran, where members of Iran's religious minorities, such as Christians or Baha'is, are buried separately from Muslims. Within Khavaran, there is a piece of unmarked land, a mass grave for the massacre victims including Amiri, her two brothers, and thousands of others killed in those dark days.

"When we went to Khavaran for first time, it wasn't like a cemetery at all, just piles of soil and crowds of mourning mothers," recalled Mohammadi.

She returned to Khavaran many times a year although she did not know her mother's exact burial site. There was also pressure from the authorities, who did not let families gather at the cemetery or hold anniversaries.

Mohammadi is hopeful the Iran tribunal will unearth the truth about those bleak years. "Imagine how a six-year-old girl could ever cope with this cruelty, hoping that these nightmares would end someday," she said. "At my age today, I can honestly say that it has got worse, this pain never heals."

Lawdan Bazargan, is another Iranian who also lost a loved one in the massacre. Her brother, Bijan, was arrested in 1982 and executed along with thousands of other political prisoners between August 1988 and February 1989, although he initially only had a prison sentence.

Bijan was buried in Khavaran. "Iranian officials did not give the bodies of the families, they did not show them their grave or their wills," she said. "Sometimes the cemetery guards would protest why we were there. They would tell us no one was buried there, that we were going for nothing.

"Every time the families were going to Khavaran, they would beat them, insult them and kick them out of the cemetery."

Bazargan said the survivors were looking for the truth. "But grief of losing our loved ones will never go away and the endless bitterness of their death will stay with us for ever. Nothing will fill their absence in our lives."