The gunman who murdered nine people at a Munich mall Friday may have attempted to lure young people to the scene of the crime with a fake Facebook post offering free food, authorities said Saturday.

Many of the victims were young people. The 18-year-old shooter, a high school student, wounded 27 others during his rampage before turning the gun on himself.

The gunman, who had Iranian and German citizenship, may have tried to attract people to the mall's McDonald's restaurant prior to the shooting using a hacked Facebook account that offered free food, Robert Heimberger, president of the Bavarian state criminal agency, said at a news conference.

"[He] said he would treat them to what they wanted as long as it wasn't too expensive — that was the invitation," Heimberger said, according to Reuters.

This line of inquiry still needs to be verified, he added.

A motive for the attack has not yet been established, but there are indications the young man had an obsession with mass shootings and that the incident could be a copycat attack. The shooting was carried out on the fifth anniversary of right-wing extremist Anders Behring Breivik's attack on a youth camp in Norway that killed 77 people. The shooter's home was found to contain literature about mass killings.

"There was material found in the apartment of the suspect that showed a particular interest in shooting sprees," said Interior Minister Thomas de Maiziere.

Authorities have said they believe the man was acting alone and there is no evidence he was connected with the Islamic State, or other extremist groups.

The mall shooting followed an ax and knife attack on passengers on a train near Wuerzburg-Heidingsfeld Monday. ISIS claimed responsibility for the crime, carried out by a 17-year-old Afghan asylum seeker.

"Such an evening and such a night is difficult to bear," Chancellor Angela Merkel said after the Munich shooting. "And it's even more difficult to bear because we have had so much terrible news in so few days."

The Associated Press contributed reporting.

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