August 31 was the 19th anniversary of the execution of thousands of Iranian political prisoners in 1988 who were buried in a mass grave in Khavaran . Friends and relatives of the victims visited the grave where their chidren, brothers, sisters are buried without name or sign.
In spite of pressure from human rights organizations like Human Rights Watch  the Iranian government has never officially acknowledged the executions. The majority of those executed were serving prison sentences for their political activities after unfair trials in revolutionary courts. They had however never been sentenced to death.
Grand Ayatollah Montazeri  who was supposed to replace Grand Ayatollah Khomeini , the Founder of Islamic Republic, once criticized this mass killing and was reportedly then marginalized by the Islamic Republic.
Azadi-B has published  30 photos of this event:
Kooshtar 67 (means killing of 67 or 88) says  [Fa] 19 years have passed since political prisoners were massacared in the summer '88. We still hope that one day that truth-finding committees may provide information, and that popular tribunals may condemn those responsible for the crime.
Azarmehr explains  what happened in the prisons before the executions:
Iran's political prisoners were called in to face kangaroo courts of three clerics. The prisoners were asked two questions each, “Do you believe in Allah?”, “Are you prepared to renounce your organisation?”. The prisoners had no idea about the consequences of their replies. In fact a ‘No’ to any of the above questions meant immediate execution. Many of the prisoners had already finished their prison sentences but were still not released, some were even brought back after they had been released.
And I know that you are not going to forget
The fate of our brothers
After many years
You will remember in a stormy night
That bloody summer
*The image above is a poster published by the Association of Political Prisoners in Exile to remember the victims