A policeman stands in front of a McDonald’s restaurant where a shooting left nine people. Picture: AP Photo/Jens Meyer

“(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, told a news conference.

Mr Heimberger said the information still needed to be verified, but there was evidence suggesting the attacker, named as 18-year-old German-Iranian Ali David Sonboly, had set up the invitation to the McDonald’s restaurant and sent it or posted it online.

It appeared he had hacked the Facebook account and invited people to join him at the McDonald’s restaurant where the massacre took place.

He used the profile of an attractive young woman to send the messages — but soon after at least one person saw through the attempt and warned people online not to fall for it.

“This here is a fake account of one Ali Sonboly. Don’t get your hopes up,” wrote Lukas Dore. “The boy is psychologically disturbed and only wants attention.”

It’s not clear how many of the victims or others at the McDonald’s had seen the post and gone there to meet him.

Ali David Sonboly went on a shooting spree through Munich before turning the gun on himself.Source:Supplied

Most of the dead were youths and all were Munich residents of varied ethnic backgrounds. Hueseyin Bayri, who witnessed one boy’s death, told The Associated Press the shooter screamed a profanity about foreigners and said “I will kill you all” as he pulled the trigger. A video shot of Sonboly also showed him yelling anti-foreigner slurs.

The fact that most of the dead were so young added to what Chancellor Angela Merkel called “an evening and night of horror.”

Mr Heimberger said investigators were still looking for a motive for the attack but Munich prosecutor Thomas Steinkraus-Koch told reporters the gunman apparently was undergoing psychiatric treatment for problems including depression. Interior Minister Thomas de Maiziere said authorities were checking reports the teen may have been bullied by his peers.

Footage showing the gunman who opened fire on the public outside a McDonald's and inside a shopping centre in the German city of Munich. Picture: Twitter/AekyanSource:Twitter

Police earlier detailed evidence found in the teenager’s bedroom after raiding the apartment Sonboly lived in with his parents.

Investigators seized a computer which will be thoroughly analysed, and discovered documents and books that suggested the attacker was obsessed with the topic of fatal rampage.

One of the books was an analysis of school shootings. An English version of the book is titled Why Kids Kill: Inside the Mind of School Shooters.

It appeared he was obsessed with mass shootings but who had no links to Islamic state or any political motivation.

Munich prosecutors said Sonboly had previously been in psychiatric care and was being treated for depression. Investigators suspect he was “deranged” at the time of the shooting.

He was armed with a 9mm Glock pistol and 300 rounds of ammunition.

Policemen stand in front of a fast food restaurant near the Olympia shopping centre a day after a gunman killed nine people in a deadly rampage. Picture: Christof Stache/AFPSource:AFP

The shooting on Friday at 6pm (Saturday 2am AEST) took place at the Olympia shopping centre in the Moosach district.

With nine people dead, about 20 others were injured and 16 people were being treated in hospital.

Sonboly’s body was found a kilometre away from the shopping centre.

Munich has a population of 1.4 million and it was in lockdown into the early hours of Saturday morning and public transport had shut down and residents were urged to stay indoors.

Hueseyin Bayri, who witnessed one teenager’s death, told The Associated Press a victim died in his arms.

“I was exactly at the spot where the boy died,” Bayri said of the victim.

“I saw that the boy beside me — I didn’t know him, but I’ve taken him into my heart — fall down.”

People mourn near the crime scene at the Olympia shopping centre where nine people were shot dead by a lone gunman. Picture: Johannes Simon/Getty ImagesSource:Getty Images

Bayri described trying in vain to keep the teen alive until help arrived.

“’Your injuries aren’t that bad, brother,’ I said to him. ‘The ambulance is already coming. Don’t worry, it’ll all work out.’ Then he died in my arms,” he told The Associated Press.

“I will never forget the last words that he told me,” said Bayri, shaking his head.

“’Please help me, please help me.”’

Monica Raduvanov was at the Munich McDonald’s where the first shots fell.

Terrified, she ran for cover beneath a bush outside the restaurant.

“I just hid and trembled and screamed,” she said.

Running into a nearby shop after a few minutes, she spent the next five hours inside until police sounded the all-clear.

“I was petrified,” she said, still shaking a day after the ordeal.