One of the attackers, Markus Sch., 18, had drunk half a bottle of vodka and five bottles of beer, while the other, Sebastian L., 17, had consumed two bottles of beer, the report said.
They allegedly beat Brunner, 50, to death in September last year after he tried to stop them bullying a group of children.
But according to sources close to the evidence in the Munich court where the case is expected to begin in April, Brunner, who had trained for at least a year in a boxing school, had thrown the first punch, striking one of the accused in the face.
The tragic confrontation began when Brunner intervened while the two accused and a third youth were attempting to extort money out of some children on an S-Bahn commuter train.
Brunner offered to escort the children out of Solln station but the accused pair followed him off the train.
Witnesses say Brunner called out to the train driver, “There's trouble back here” before the violence began on the train platform.
There appears to be conflicting accounts from witness concerning who was aggressive, according to Spiegel. However, witnesses said the attack by the accused was particularly brutal.
Markus Sch. used a bunch of keys as a weapon while Sebastian L. held a cigarette lighter in his fist while he struck Brunner, the report said. They continued to punch and kick Brunner even after he had struck his head on a metal handrail and fallen to the ground.