Who is Kamal and what happened to him?

For a week they stay in a basement with other refugees. Amir recognizes Kamal, who looks sickly and depressed, and Kamal’s father. Amir overhears Kamal’s father telling Baba what happened to Kamal that made him so weak. Four men caught Kamal out, and when he came back to his father he was bleeding “down there” (p. 120). Kamal no longer speaks, just stares.