The 18-year-old who shot and killed 10 people on Friday night in Munich is believed to have planned his attack for a year, Bavarian investigators told reporters on Sunday.
He also wrote a manifesto that police say is still being evaluated.
The suspect, identified as Ali Sonboly, died from a self-inflicted gunshot wound and was of dual German-Iranian nationality, police confirmed on Saturday.
His body was found more than two hours after the attack. He was carrying a 9-mm Glock pistol and still had some 300 rounds of ammunition on him when he shot himself, police said Saturday.
Photos from the scene:
Shooting in Munich shopping center
Shooting in Munich shopping center
A scrren grab taken from video footage shows special forces police officers walking along a street outside the Olympia shopping mall following a shooting rampage in Munich, Germany July 22, 2016. REUTERS/Reuters TV
A screen grab taken from video footage shows police officers near the Olympia shopping mall following a shooting rampage in Munich, Germany July 22, 2016. REUTERS/Reuters TV
A police officer stands guard at the main train station following a shooting rampage at the Olympia shopping mall in Munich, Germany July 22, 2016. REUTERS/Michael Dalder
Special force police officers stand guard at an entrance of the main train station, following a shooting rampage at the Olympia shopping mall in Munich, Germany July 22, 2016. REUTERS/Michael Dalder
MUNICH, GERMANY - JULY 22: Police officers escort people from inside the shopping center as they respond to a shooting at the Olympia Einkaufzentrum (OEZ) at July 22, 2016 in Munich, Germany. According to reports, several people have been killed and an unknown number injured in a shooting at a shopping centre in the north-western Moosach district in Munich. Police are hunting the attacker or attackers who are thought to be still at large. (Photo by Joerg Koch/Getty Images)
MUNICH, GERMANY - JULY 22: An armed police officer points his gun in front of a mall were a shooting took place in Munich, Germany on July 22, 2016. Several people have been killed on Friday after an unknown number of assailants opened fire in a shopping mall in the southern German city of Munich. (Photo by Sebastian Widmann/Anadolu Agency/Getty Images)
Police sign blocks the entrance to Odeon square following shootings at a shopping mall earlier on July 22, 2016 in Munich.
Six people were killed and several gravely injured on Friday in a shooting rampage at a Munich shopping centre, with the attackers still believed to be at large. / AFP / dpa / Sven Hoppe / Germany OUT (Photo credit should read SVEN HOPPE/AFP/Getty Images)
Police secures the area inside a shopping center in Munich on July 22, 2016 following a shooting.
At least one person has been killed and 10 wounded in a shooting at a shopping centre in Munich on Friday, German police said. / AFP / STR (Photo credit should read STR/AFP/Getty Images)
Police secures the entrance to a subway station near a shopping mall where a shooting took place on July 22, 2016 in Munich.
Several people were killed on Friday in a shooting rampage by a lone gunman in a Munich shopping centre, media reports said / AFP / dpa / Lukas Schulze / Germany OUT (Photo credit should read LUKAS SCHULZE/AFP/Getty Images)
Police and firefighters are seen near a shopping mall amid a shooting on July 22, 2016 in Munich.
Several people were killed on Friday in a shooting rampage by a lone gunman in a Munich shopping centre, media reports said / AFP / dpa / Matthias Balk / Germany OUT (Photo credit should read MATTHIAS BALK/AFP/Getty Images)
Special force police officers stand in front of a car near the Olympia shopping mall, following a shooting rampage at the mall in Munich, Germany July 23, 2016. REUTERS/Michael Dalder
QUALITY REPEAT - Special forces police officers stand guard at an entrance of the main train station, following a shooting rampage at the Olympia shopping mall in Munich, Germany July 22, 2016. REUTERS/Michael Dalder TPX IMAGES OF THE DAY
Police officers are pictured at the entrance of an appartment building following a shooting rampage at Olympia shopping mall in Munich, Germany July 23, 2016. REUTERS/Michael Dalder
People are evacuated from the area around the shopping mall Olympia Einkaufzentrum OEZ in Munich on July 22, 2016 after gunmen went on a shooting rampage in the busy shopping centre, killing eight people in a suspected terror attack.
The southern city was in lockdown after the shootings, which saw panicked shoppers fleeing the Olympia mall as armed anti-terror police roamed the streets in search of the assailants.
/ AFP / STRINGER (Photo credit should read STRINGER/AFP/Getty Images)
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There were fears the attack was motivated by a radical Islamist ideology of the kind apparently held by the attackers in the recent terror attacks in southern Germany and Nice, France, which were both claimed by the Islamic State group. But prosecutors say the attack does not appear to be explicitly political in motivation.
"We consider this to be a classic lone gunman without political motivation," Thomas Steinkraus-Koch, Munich's chief prosecutor, said in a press conference on Saturday.
Munich Police Chief Hubertus Andrae also said that based on police searches of Sonboly's home, " there are no indications whatsoever that there is a connection to Islamic State."
Sonboly, who was not previously known to police, apparently suffered from depression and was receiving psychiatric treatment. A 14-year-old who went to Sonboly's high school told The New York Times' Rukmini Callimachi that Sonboly had been severely bullied at school.
"She claims that he had an altercation several months ago with a classmate at school and threatened to 'go on a shooting rampage,'" Callimachi reported.
Still, Sonboly's motive remains "fully unclear," Andrae said. He had evidently researched previous killing sprees, prosecutors said. A book entitled "Rampage in Head: Why Students Kill," was found during searches of the home he shared with his parents in Dachauer Strasse, in the Munich suburb of Maxvorstadt.
His parents are "too shocked to help with the investigation" at this time, police said.
Police also said there was an "obvious link" between Sonboly and Norway's mass killer Anders Behring Breivik, who murdered 77 people in July 2011. Sonboly's shooting spree in Munich coincided with the fifth anniversary of the Norway massacre.
He apparently lured victims to the McDonald's where he opened fire after setting up a fake Facebook page under a woman's name and promising people free food if they showed up.
"(He) said he would treat them to what they wanted as long as it wasn't too expensive - that was the invitation," Robert Heimberger, president of the Bavarian state criminal agency, said in a press conference Saturday.
Three 14-year-olds and two 15-year-olds are among those who were killed. The other victims were 17, 19, 21 and 45 years old, police said.
The shooting was the second high-profile incident of violence in Germany this week. On Monday a teenager attacked four people with an ax on a train in southern Germany. ISIS claimed responsibility for the train attack.
"For the second time in a few days we've been shaken by an incomprehensible bloodbath," Bavarian Premier Horst Seehofe told reporters Saturday. "Uncertainty and fear must not be allowed to gain the upper hand."
German Chancellor Angela Merkel will convene her security council on Saturday to address the shooting, according to AFP. The council consists of several top German officials, including the ministers of defense, interior affairs, and foreign affairs.