Ali David Sonboly, who carried out the July 22 Munich shooting spree that left nine persons dead, had reportedly visited Iran with his father for a weapon's training stint before carrying out the attack
News magazine Focus said that the 18-year-old with a dual German-Iranian citizenship underwent "weapons training" in Iran in December 2015, Mirror.co.uk reported.
The shooter's family moved to Munich two years ago from Iran.
Sonboly, who was obsessed with violent computer games, bought a 9mm Glock handgun from the 'dark web' for 80 pounds ($104) to carry out the attack, Mirror.co.uk said.
The shooter, who left over 20 others injured, was obsessed with Adolf Hitler and expressed shocking racist views, German investigators have said.
The Munich prosecutor's office refused to comment on the report saying: "We cannot make any comment on this aspect of the case due to the ongoing enquiry."
Sonboly's body was found on a side street close to the shopping centre where he reportedly committed suicide.