After a search of the family home of the German-Iranian 18-year-old in the Maxvorstadt neighbourhood, police say they have found evidence which indicates an Amoklauf (lone rampage), the Süddeutsche Zeitung reports.
The Chief of Police in Munich said that the 18-year-old, who killed nine other people, had no relationship to terror group Isis.
Among other things police found newspaper articles and books which covered police operations during previous gun sprees.
According to BR one of the books was called 'Rampage - why students kill.'
Prosecutors said he seems to have been fascinated by gun sprees and believe that he had no other motive for his act.
Prosecutor Thomas Steinkraus-Koch said that the young man was likely suffering from a mental illness, possible depression.
State police have said that he was carrying 300 rounds of ammunition and that his gun was a Glock.
A postmortem on the killer suggest that he killed himself, as had been speculated during the night. It showed that he only had one bullet wound to the head.
According to BR, most of his victims were adolescents, including three with Kosovan nationality. Two of the victims were 15 year olds, three were 14 year olds and the others were 17, 19, 20 and 45 years of age.
Nine people were killed and another 16 wounded as the black-clad gunman brought terror to Germany's third largest city on Friday evening, before committing suicide.
"Bloodbath in Munich," was the headline on the best-selling Bild newspaper as shockwaves reverberated across the continent.
The killing spree sent the southern city into lockdown as elite police launched a massive operation to track down what had initially been thought to be up to three assailants.