Complex sentence: In 1948 he was arrested, tried and convicted for murder for the execution by firing squad of a drunk artillery colonel without proper trial while Balck was serving as commander of Army Group G on the western front in 1944.
Split into simpler sentences: In 1948 he was arrested, tried and convicted for murder for the execution by firing squad, without proper trial, of an artillery colonel who was found drunk on duty. This incident occurred while Balck was serving as commander of Army Group G on the western front in 1944.