From Aghelane:

Karroubi went to the Ghoma Mosque for the annual mourning over the death Ayatolla Dr. Seyyed Mohammad Hosseini Beheshti, the former Secretary General of the Islamic Republic Party. He and around 70 members of IRP were assassinated in 1981 in a bombing by the People's Mujahedin of Iran. The government won't permit gatherings for protests or mournings for slain protesters, so Karroubi encouraged protesters to come to this gathering instead. Mousavi couldn't make it.