On a perfect mid-autumn day, the scene at an upscale suburban mall in Sydney, Australia, was as humdrum as it was idyllic: mothers pushing strollers, gaggles of teenagers being young, families whiling away the weekend afternoon.

But in a matter of minutes on Saturday, the sprawling, multistory mall instead became a site of panic, chaos and terror. Only a mile from the famous Bondi Beach in eastern Sydney, a knife-wielding attacker stabbed nearly 20 people, including a 9-month-old girl. Six of the victims, including the girl’s mother, died, and about a dozen others were being treated at hospitals. The attacker — whose motives remain unclear — was shot and killed by a police officer.

It was one of the deadliest mass killings in Australia in recent decades, and has left many in shock, questioning how a tragedy of this magnitude could occur in a country known for its relative safety.

People in the surrounding community said the violence was all the more unsettling because the mall was such a hub of life that everyone had just been to, or was about to visit. Familiar backdrops — the Lego store, a boba stand, clothing shops — had become crime scenes and parts of traumatic memories.

“These things don’t happen in Australia,” said Kristie Spong, 54, who had been to the mall with her daughter a few days earlier and returned Sunday to lay flowers, her makeup running down her face through tears. “We just think we’re a blessed country because we have good gun control.”

The police on Sunday were combing through a crime scene spanning several floors of the Westfield Bondi Junction mall, which remained cordoned off. They were also going through footage from numerous CCTV cameras and interviewing hundreds of witnesses to Saturday’s attack, trying to piece together the chronology of a rampage that punctured a sense of security in this wealthy suburb of Australia’s largest city.