The Munich gunman appears to have researched mass killings before the Friday evening massacre.
A search of David Ali Sonboly's room has indicated he was obsessed with mass killings, with police ruling out links to the Islamic State.
During the search of his room, investigators found a book called 'Rampage in Head: Why Students Kill'.
US psychologist Peter Langman, who wrote the book, said that many juvenile killers "often research other shooters and find a role model".
He said his book was written "to keep people safe, to teach people what to look for to prevent such attacks".
Police are investigating whether Sonboly, 18, specifically targeted young victims as he rampaged through McDonald's and the Olympia shopping centre armed with a Glock pistol and 300 rounds of ammunition.
Most of those killed were teenagers.
It was reported four of those who died were young friends sitting at the same table in the fast food restaurant.
They were two 14-year-old Kosovan girls, Armela Segashi and Sabina Sulaj, and their Turkish friends Can Leyla, 14 and Selcuk Kilic, 15.
Another victim named as 17-year-old Hussein Daitzik, of Greek origin, is reported to have been shot dead as he shielded his sister.
Guilliano Kollman, 18, is said to have died after being gunned down outside the McDonald's.
Armed police move past onlooking media responding to the shooting | Photo: PA Images
Naim Zabergja, a policeman of Kosovan heritage, visited the scene of the shooting clutching a picture of his 21-year-old son Dijamant, who was killed in the rampage.
Sevda Dag, a 45-year-old Turkish woman, was reportedly the oldest victim of the atrocity.
Meanwhile, Fadil Segashi, the uncle of Armela, said she was "an example to others".
He added: "She was only 14-years-old and she was a very good girl."
A third victim from Kosovo has been named as Sabina Sulaj.
Breivik massacre
Authorities are checking reports that he felt bullied by his peers for several years, Interior Minister Thomas de Maiziere said.
Police said it appeared the teenager hacked into a Facebook account and lured people to McDonald's with an offer of free food.
The posting had been sent from a young woman's account.
It urged people to arrive at the centre at 4pm, saying: "I'll give you something if you want, but not too expensive."
It has also been reported Sonboly swapped his WhatsApp profile picture to that of mass murderer Anders Breivik.
Far-right extremist Breivik killed 77 people in Norway exactly five years to the day of the Munich shootings.
Bavarian Interior Minister Joachim Herrmann said: "The fifth anniversary of the Breivik massacre ought to be considered as a motivation."
