Judge Darko Samardzic said the court had not been informed as to whether the defendant received his summons or changed his place of residence.
Defense attorney Radivoje Lazarevic said that he last spoke to the defendant when he was appointed his ex-officio defense attorney.
Maksimovic, who resides in Serbia, has been charged with killing five Bosniak civilians, including three children, in Caparde in the municipality of Osmaci in June 1992. It is alleged that he committed these crimes as a former member of the Bosnian Serb Army.
A new plea hearing has been scheduled for September 16.