The crimes Tandro accused Dax of were those of Curzon Dax, who he believed had betrayed his father to rebel forces during the Klaestron Civil War. In truth, however, Curzon and his father had been great friends and Curzon had never provided an alibi in order to spare the General's widow, Enina Tandro the embarrassment of admitting her affair with Curzon.
Enina admitted the affair, in part to spare Jadzia, but also to force Ilon to allow his obsession with his father to finally die. When Ilon Tandro learned this, he dismissed the charges against Dax. It was not clear if he was forgiving toward his mother as well, since his first instinct was to pull away from her. (DS9: "Dax")