Video from the aftermath of the deadly shooting spree in Munich on Friday shows an onlooker engaged in a shouting match with the gunman, 18-year-old Ali Sonboly.
The footage was taken by a resident of a nearby apartment on his cellphone.
The resident, identified by the Bild newspaper as Thomas Salbey, said he had been drinking a beer on his balcony when he heard the gunshots.
"I looked down from my balcony and saw how the man went through the glass entrance-way. He had reloaded his pistol. I threw my beer bottle at him. It shattered on the glass roof. But I think he didn’t hear it anyway," he told the German daily.
Salbey then hurled insults at Sonboly, at one point shouting "Are you crazy!?" to which the gunman responded: "I'm German."
"You’re a w****r is what you are," Salbey can be heard replying.
Sonboly responded with a volley of bullets at Salbey, damaging his balcony but missing the man himself.
"I was not scared. I didn’t know whether they were real bullets or just rubber bullets," Salbey explained.
The teenage gunman is believed to have shot himself dead with the same Glock 9 mm pistol he used to murder nine people and injure many more.