Although he was too young to have any real recollection of his father, Ilon grew up venerating his father's memory, and was determined to find his murderer.
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; old military records had been recently disclosed which suggested that Curzon Dax had been responsible for sending the transmission that resulted in Tandro being caught. 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; at the time the transmission was sent, she and Curzon had been in bed together.
Enina admitted the affair, in part to spare Jadzia from suffering for Curzon's alleged crime, 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")