The 51-year-old is said to have been suffering from psychological problems and under the influence of alcohol when he sped down a pedestrian street in the run-up to last Christmas.
Alongside five murder charges, the man, whose name has not been released by authorities, faces 18 counts of attempted murder and another 14 of grievous bodily harm.
Judges in the city’s regional court will determine whether the man, about whom little is known publicly, was wholly or partially responsible for the acts, owing to his known psychiatric issues.
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An expert evaluation prepared ahead of the trial determined that the accused suffers from psychosis, and according to police, could only give an approximate and sometimes contradictory account of events.
Investigations by the police at the time ruled out any political, terrorist or religious motive.
Rather, the man is said to have been frustrated by his personal circumstances.
Sitting at the wheel of his SUV, the man indiscriminately targeted passers-by with the intention of killing or injuring as many as possible, according to the indictment.
The vehicle travelled between 600 metres and one kilometre at high speed, causing panic and leaving a trail of broken glass and debris along the city’s cobbled streets.
After coming to a stop, the man stepped out of his car and was arrested.
Among the victims were a nine-week-old baby girl and her father, 45, while the infant’s mother and the couple’s one-and-a-half-year-old son survived with serious injuries.
A 73-year-old woman, a 52-year-old cyclist and a student, 25, were among the others killed.
“It’s a horror scene,” a police spokesperson told reporters following the events, in which many of the survivors were left traumatised.
The trial is set to continue until at least January.
Police inspect the scene of the crime in the centre of Trier on December 1st, 2020. The man is said to have been under the influence of alcohol when he allegedly ran into the shoppers. Photo: Jean-Christophe VERHAEGEN / AFP
Germany has seen a number of vehicle rampages in recent years in which the drivers suffered from psychological problems.
The most deadly of these took place in January 2019, when a German injured eight people when he drove into crowds on New Year’s Eve in the western cities of Bottrop and Essen. He was later taken into psychiatric care.
The events in Trier also brought back memories of the Islamist attack at a Berlin Christmas market in 2016 that killed 12 people.