The gunman who opened fire inside a Munich shopping center Friday killing 9 people sent out an online invitation about a bogus free giveaway to attract more people to the site of the attack, investigators said.

The gunman hacked a Facebook account and sent a message urging people to come to the Olympia Einkaufszentrum mall for a free giveaway, a police investigator said.

The posting, sent from a young woman's account, urged people to come to the mall at 4 p.m., saying: "I'll give you something if you want, but not too expensive." Police believe the gunman sent the message.

The motive behind the shooting remains unclear, despite early reports indicating it appeared to be terror related.

Munich police chief Hubertus Andrae says "no evidence" of links to the Islamic State group has been found in the home and room of the Munich shooting suspect.

Andrae also told a news conference that the crime and the perpetrator had "absolutely no" link to the issue of refugees.

Peter Beck, a Munich police spokesman, said officers were still collecting evidence at the scene of the crime Saturday morning.

"With regard to the suspect we have to examine everything, but we don't know yet what triggered the crime," Beck told The Associated Press.

Beck said the number of people receiving hospital treatment stood at 16, three of whom were seriously wounded. Security restrictions in the city have been lifted and public transport is operating as normal, Beck said.

The suspect was identified as an 18-year-old German-Iranian man, who was born and raised in Munich. Prosecutor Steinkraus Koch tells a news conference the suspect had a book titled: "Rampage in Head: Why Students Kill."

Police Chief Andre says that the suspect appeared to be "obsessed with shooting rampages."

Investigators also found evidence that the Munich-born suspect had suffered from psychological problems and received treatment, but details were still being confirmed, Steinkraus-Koch said.

Some 2,300 police from across Germany and neighboring Austria were scrambled in response to the attack, which happened less than a week after a 17-year-old Afghan asylum-seeker wounded five people in an ax-and-knife rampage that started on a regional train near the Bavarian city of Wuerzburg. The Islamic State group claimed responsibility for the train attack, but authorities have said the teen -- who was shot and killed by police -- likely acted alone.

The suspect's body was found about 2 1/2 hours after the attack, which started shortly before 6 p.m. at a McDonald's restaurant across the street from the mall.

A cell-phone video posted online showed the suspect dressed in black standing on a rooftop parking area of the mall yelling back and forth with the person filming, saying at one point "I'm German" and eventually firing shots. Andrae said police believe the video is genuine.

David Akhavan, a 37-year-old who from Tehran, Iran, who works at the Shandiz Persian restaurant, described his anguish as he learned of the shooting.

"I started to get texts from friends asking if I was safe," he said. "Then, my thoughts were: please, don't be a Muslim. Please don't be Middle Eastern. Please don't be Afghan. I don't accept any of this violence."

The mayor of Munich has declared a day of mourning for the victims of Friday's shooting in the Bavarian capital. Dieter Reiter says the city is "shocked and aghast at this terrible act."

In a statement Saturday on Facebook, Reiter expressed his condolences to the victims, their family and friends, and thanked security forces for their work.

Ten people, including the alleged shooter, were killed in the attack.

Reiter said Saturday would be "a day of mourning, not of celebration" and that all public festivals in the city over the weekend had been canceled.

"These are difficult hours for Munich," he said, adding that the city's citizens had shown great solidarity toward each other. "Our city stands united."

The Associated Press contributed to this report.