The lone teenager who shot dead nine people and injured 27 others in Munich had researched school killing sprees and attempted to lure victims to the scene of his rampage with an offer of free food on social media, officials have said.

Police said the 18-year-old gunman, who opened fire at a crowded shopping centre and McDonald’s restaurant on Friday evening, had been raised in Munich and was still in full-time education.

They added that he had likely been in psychiatric care and there were indicators he had been treated for depression.

Robert Heimberger, a police investigator, said on Saturday it appeared the gunman had hacked a Facebook account and lured people to the shopping centre with an offer of free food.

The post, sent from a young woman’s account, urged people to come to McDonald’s at 4pm, saying: “I’ll give you something if you want, but not too expensive.”

“It appears it was prepared by the suspect and then sent out,” Heimberger said.

The gunman, who has been identified as Ali Sonboly, is said to have researched mass-casualty attacks and had an obsession with shooting sprees, including the 2011 massacre in Norway carried out bythe rightwing fanatic Anders Behring Breivik.

Classmates of Sonboly told the Guardian he had been bullied at school, while neighbours described him as shy and lazy. “At school, Ali was often bullied by others and really unpopular,” one classmate said. “He was a bit chubby, and he was either by himself or together with one or two people, but he seemed to have hardly any friends.

“Yesterday at noon, I came home and I saw Ali here in the entrance of our building, he was still delivering newspapers the day of the shooting. It was strange though because he usually at least says hi to me because I do know him, but when I greeted him, he didn’t say a word to me and seemed strange and withdrawn.”

Officers remained at the scene on Saturday morning collecting evidence and others were seen searching an apartment in the city’s Marxvorstadt district believed to be owned by the gunman’s parents.

Officials said the searches had revealed no links to Islamic State, and suggested the attack was unlikely to have been motivated by Islamist extremism. They said they had found newspaper clippings and books related to killing sprees, one of which was believed to be a textbook called Why Kids Kill: Inside the Minds of School Shooters.

Police spokesman Peter Beck said officials “don’t yet know what triggered the crime” but that there was no clear political motivation.

Stephan Baumanns, owner of the Treemans bakery and coffee shop below Sonboly’s apartment, said: “I saw [Sonboly] every once in a while pass by, he was a very shy guy and tall, about 6ft 2in (1.88m). He wasn’t very sporty, rather a little chubby.

“He seemed like a lazy guy. He had a job distributing a free newspaper, Münchener Wochenblatt, but I often saw him rather than deliver them, throw them all away into the garbage bin.”

Police also confirmed the victims killed in the massacre included two 13-year-olds. They said they had not yet established whether young people had been deliberately targeted.

Munich police chief Hubertus Andrae said the attack “makes us speechless and our thoughts go out in particular to the victims.

“As a result of the manhunt with a large-scale operation force we have found a male person, who given the current level of intelligence committed suicide. On the basis of witness reports and on the basis of CCTV footage we assume that this person is the suspect.

“We currently have no indications that there were further perpetrators involved. The suspect is, according to the current level of intelligence, an 18-year-old Iranian from Munich.”

The gunman was carrying a 9mm Glock handgun, and a red rucksack containing 300 rounds of ammunition, police said.

Police have appealed to witnesses who filmed the attack to pass the footage to them. Unverified clips posted on social media appeared to show a man shouting slogans; another appeared to show people running for their lives as a man opened fire on pedestrians.

Police first received reports of a shots being fired near the Olympia shopping centre at around 5.50pm local time on Friday. The attacker opened fire in the McDonald’s on Hanauer Street with the handgun.

From there the suspect moved into the shopping centre, police said. Armed units flooded the area, with officers in plain clothes seen running through the shopping centre in search of the gunman. More than 800 officers remain engaged in the investigation, police said.

The gunman’s body was found in a side street close to the shopping centre at around 9.30pm local time. Police said they believed the teenager had killed himself, although Andrae said a postmortem examination was needed to see if he died as a result of officers’ gunfire.

Officers recovered weapons with “relatively large” magazines at the scene, contrary to earlier suggestions that long-barrelled guns were used. Andrae also dismissed earlier fears that there were up to three gunmen involved in the attack triggered by two bystanders fleeing in a car at “considerable speed”.

There were reports of people barricading themselves in stores in the shopping centre as the attack unfolded and Munich was put into lockdown. People on the streets were urged to run and find refuge, public transport was shut down and motorists were told to clear the city’s roads and motorways to give clear passage for the emergency services.

Locals offered their homes as safe havens using the hashtag #OffeneTur (open door) and invited people left stranded by the emergency response to stay.

Around 2,300 police officers were deployed on the city’s streets and specialist counter-terror units were flown in. Police forces in neighbouring Austria and Switzerland also sent officers to assist.

Angela Merkel was due to meet her chief of staff, interior minister, and a host of intelligence officials on Saturday morning to review the incident, which comes in the wake of the Bastille Day truck atrocity in Nice and an axe attack in Bavaria.

Bavaria’s state premier, Horst Seehofer, was visibly emotional as he said it was the second time in six days that he has had to give a statement about a terror attack. He thanked the world for their messages of sympathy and insisted: “We have to continue to live our lives and our values.”

Jamie Grierson, Emma Graham-Harrison, and Kate Connolly and Janek Schmidt in Munich

Additional reporting by agencies