People lay flowers and candles outside the OEZ shopping center the day after a shooting spree left nine victims dead on Saturday, July 23 in Munich, Germany.
Munich mourns mall shooting victims
02:13 - Source: CNN

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Gunman had visited and photographed site of a 2009 mass shooting, officials say

Documents confirm the gunman suffered from mental illness, police say

CNN  — 

The gunman who killed nine people in a rampage in Munich on Friday was obsessed with mass shootings and appeared to have planned the attack for a year, officials said.

“He appears to have planned this act since last summer,” Robert Heimberger, president of the Bavarian state criminal police office, said at a press conference Sunday.

“He completely occupied himself with this act of rampage.”

Police have not named the attacker. They said he was an 18-year-old with dual German and Iranian nationality who was born and raised in Munich. Neighbors told CNN Saturday that a teen named Ali Sonboly lived in an apartment searched by police, the same name reported by German media outlets.

On Sunday, a 16-year-old Afghan believed to have been a friend of the attacker was arrested on “suspicion of being an accessory,” Munich police said.

Police said Saturday the attacker was a mentally troubled individual who extensively researched rampage killings, and had no apparent links to terror groups and no political motive.

On Sunday, investigators revealed he left behind a long written statement on his computer, which was still being analyzed. They said they found photographs on his camera showing he visited the German town of Winnenden, the site of a deadly 2009 school shooting.

Earlier, officials said they found in the gunman’s belongings numerous documents on mass killings, including a book entitled “Rampage in My Mind – Why Students Kill.”

Officials believe there likely was significance in the timing of the attack, which came five years to the day since Anders Behring Breivik killed 77 people in Norway in 2011, many of them attendees at a youth camp.

Gunman had received psychiatric treatment

The gunman had also been under psychiatric care in a hospital for two months in 2015, officials said Sunday.

Documents found in his home confirmed that he suffered from mental illness, including depression and anxiety, Munich prosecutor Thomas Steinkraus-Koch said Sunday.