Society needs to offer more support for people with psychological problems, German President Joachim Gauck said Sunday at a memorial in Bavaria's parliament for the victims of this month's deadly shooting in Munich.
"Society must not abandon these people, especially young people, and accept that they turn into dangerous outcasts," Gauck said, adding that society must consider the causes that lead individuals like the Munich shooter to murderous actions.
Eighteen-year-old Ali David Sonboly, who shot and killed nine people at a McDonald's restaurant and a nearby shopping centre in Munich on July 22 before turning the gun on himself, had been suffering from depression, according to German prosecutors.
Doctors also found antidepressants in his blood at the postmortem.
The teen had been bullied at school and also expressed racist ideas, his family and investigators said.
In an interview published ahead of Sunday's memorial service, Sonboly's father revealed that the family had been receiving death threats.
"We are receiving death threats. My wife has been crying for a week. Our life in Munich is finished," Masoud Sonboly told popular German tabloid Bild am Sonntag.
The father reproached himself for not knowing more in the lead-up to the shooting spree.
"I did not know about the gun," the taxi driver told the paper.
Masoud Sonboly also did not know that his son had been collecting information on Norwegian far-right terrorist Anders Behring Breivik, who is serving a 21-year jail term for his rampage five years ago, which left 77 dead.
The father said he was aware that his son had been bullied at school four years ago. "I removed Ali from the school and talked to his teacher," he said, adding that he also reported several of the bullies to the police. But nothing had come of the inquiries.
"I want to know all of it. I also want to know what medication my son was on," he said. Doctors had found traces of antidepressants in Ali's blood at the postmortem.
According to Sonboly, his son had become very withdrawn and spent a lot of time in his room playing violent computer games.
The family eventually moved to Maxvorstadt, a wealthy district of Munich.
Their son became obsessed with the idea that he shared his birthday with former German Nazi dictator Adolf Hitler, and the Iranian-German teen also wanted a German first name, calling himself David.
According to the paper, the teenager saw himself as an Aryan to distinguish himself from the Turks and Albanians living in his neighbourhood. Most of his victims had been teenagers with a non-German heritage.