MUNICH — The gunman whose rampage at a Munich mall left nine people dead was a depression-plagued teenager who avidly read books and articles about mass killings and apparently tried to lure young victims to their deaths through a faked Facebook posting, authorities said Saturday.

Witnesses indicated that his hatred of foreigners might have played a role in the mass shooting, even though he himself was the German-born son of Iranian asylum-seekers.

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 the perpetrator also showed him yelling anti-foreigner slurs.

The 18-year-old high school student from Munich with Iranian and German citizenship also wounded more than two dozen others Friday night before turning his illegal Glock 17 pistol on himself, ending a shooting rampage that could have become even more tragic.

Police told reporters that a search of the red backpack lying next to his black-clad corpse revealed that the shooter was carrying more than 300 rounds for the 9-millimeter handgun he used to kill his victims.

The filed-off serial numbers of the Glock made it difficult to establish its origin. But investigators said the gunman, identified by German officials only as David S., had no permit to carry it.

One victim was 45, another 20 and the rest were between 14 and 19, Munich police chief Hubertus Andrae said. The fact that most of the dead were so young added to what Chancellor Angela Merkel called ‘‘an evening and night of horror.’’

It started as a normal Friday evening. A Munich mall was buzzing with shoppers, and across the street, customers were enjoying a meal at a McDonald’s restaurant.

Earlier that day, the shooter hacked a Facebook account and sent a message inviting people to come to the mall for a giveaway, said Robert Heimberger, the head of Bavaria’s criminal police.

Investigators say they are still looking for a motive for the attack but Munich prosecutor Thomas Steinkraus-Koch noted 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.

Witnesses and a dramatic cell-phone video that police think is genuine indicated the gunman was unstable and disliked foreigners.

The shooter yelled anti-foreigner slurs both at a person verbally sparring with him from a balcony, which was caught on film by a neighbor, and later also inside the mall.

At another point, he yells, ‘‘I'm German!’’ to which the man on the balcony, identified by the Bild newspaper as Thomas Salbey, a 57-year-old construction worker, responds, ‘‘You are a jerk!’’ and demands to know what he is up to, saying ‘‘you should be in psychiatric care.’’ The gunman orders the filming to stop, and shortly after that starts shooting, causing the neighbor filming to duck.

Law enforcement officials think the Munich tragedy could be a copy-cat attack, considering it was carried out on the fifth anniversary of the killing of 77 people by Norwegian right-wing extremist Anders Behring Breivik, whose victims included dozens of young people.

A search of the shooter’s home revealed a trove of literature about mass killings, including a German-language translation of the English book ‘‘Why Kids Kill: Inside the Minds of School Shooters.’’

De Maiziere said the shooter had researched a 2009 school shooting in Germany as well as the Breivik attack.