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Tim Kretschmer was not on anti-depressants.
He was however obsessed with guns. His father was a member of the local gun club and often brought his son there to practise with various kinds of guns. Kretschmer was bullied at school, felt left out and loved to play violent computer games. See also: http://www.guardian.co.uk/world/2009/mar/11/german-school-killings-kretschmer...