Why were the men who come to Marjane's house imprisoned and tortured?

A few days after the Shah steps down, the political prisoners are released. Marjane’s family knows two of them, Siamak Jari and Mohsen Shakiba. Both had been convicted of being communists. Siamak’s wife is Mrs. Satrapi’s best friend. One day, Laly, Siamak’s daughter, visits Marjane and Marjane tells her that her father is dead and not away on a trip, as she had been told. Laly runs to her mother and Marjane is punished for saying such a thing. Marjane thinks, “Nobody will accept the truth.”

Then, when the prisoners are released, Siamak comes to visit and Marjane sees that she has been wrong. Siamak is relieved to see his family and friends once again. Soon, Mohsen joins them. They nonchalantly retell their stories of torture and abuse. Their fingernails had been pulled out and the bottoms of their feet had been whipped with electrical cords. The torturers had been trained by CIA agents, so they “knew each part of the body” and how to cause the most pain. Marjane’s parents are so shocked that they forget to tell Marjane to leave the room. One of their friends, Ahmadi, who had been a member of the guerilla army, had been captured and tortured in especially awful ways. The torturers burned his back with an iron. Marjane looks at their house iron and says that she “never imagined that you could use that appliance for torture.” In the end, Ahmadi was killed and they cut him to pieces.