Expat Lee John Heath died in hospital two days after the nightclub beating which left him with horrific head, neck and internal injuries. Doctors carried out a series of operations but could not save him.
His mother, brother and sister sat opposite the accused as the trial began on Wednesday.
The four security personnel, aged between 20 and 36, were on duty at the “U 60311” techno club when they apparently attacked Heath early on Easter Monday morning last year.
Three are charged with manslaughter, another with failing to assist Heath as he lay on the ground.
According to state prosecutors, the incident arose at around 6:15am out of an argument between another guest at the club and one of the bouncers. As the bouncer attempted to pull the man away from the bar, he apparently fell into Heath, who had nothing to do with the row.
The bouncer then attacked Heath, and was joined by two colleagues, who until then had been standing at the door. The three men beat Heath unconscious, then carried him up the stairs to the entrance and dumped him on the pavement.
Passers-by discovered the 31-year-old Briton soon afterwards and called an ambulance, where he was resuscitated. He underwent six operations on his severely damaged internal organs in the following hours.
CCTV footage of the incident was subsequently released on Facebook.
Speaking to the Local last year, Heath’s mother Marie described her son as a football fan who had moved to Germany to build a new life for himself and his long-term German girlfriend.
He was an active member of The Local’s forum Toytown Germany, and an in-demand handyman who wanted to start his own business.
“Lee didn’t deserve this but he fought to the end,” said his mother. “I have to be his voice.”
The Frankfurter Rundschau newspaper reported that the four accused did not speak during the proceedings.
The role of the youngest bouncer remains one of the biggest unknown factors in the incident.
The 20-year-old apparently did not take part in the beating itself, but the paper reported that he may have stopped other guests from intervening, and helped to carry Heath out of the club.
His defence lawyer says he was legally a minor at the time, and called for his trial to be separated from that of his co-defendants and brought before a juvenile court.
The trial is expected to last at least until June – more than 20 witnesses have been called.