Witnesses spotted Sourian behaving strangely as he wandered through Hornsby Mall outside Westfield before the shooting.
Ku-Ring-Gai art teacher Raquel Redmond said she noticed him just before the incident took place. "I was in front of this poor ... man," she wrote in an emotional Facebook post. "His arms were holding down and on his left hand he was holding a small instrument.
"Then the police, in front of me, came into my focus when he shouted 'drop it', the police was (sic) holding a gun.
"I realised it was a serious situation and I run to find a place to hide. From there I saw many police running and holding guns and I heard a woman screaming. Then, there were four very fast shots, result: four people shot, the ... man and three bystanders. Sad that this is happening right here in this village.
"I saw this old couple staring at him and that's when I realised he had a full knife," local restaurant manager Geoff Milner told the Hornsby Advocate.
James Yeom, who works at a store in the area, told Seven News: "He looked really depressed. He wasn't looking too aggressive, he was just wandering around."
A Hornsby resident, who did not want to be named, told news.com.au he spoke to the knifeman shortly before the incident.
"I noticed a chap walking around talking to himself, I do a lot of work with the homeless and I asked him if he was OK, he just looked at me and walked away," he said. "I noticed that he had a knife but I just thought he was one of the traders."
The shopper said traders often had knives to cut their produce at the fresh fruit and vegetable markets at the shopping centre.
"Apart from the babbling, he didn't look different," the resident said of the man. "He looked dishevelled, but who doesn't on a Thursday morning?"
The resident described the knife as quite large, probably at least 13cm long, and said it looked like an ordinary cutting knife that you would use in the kitchen.
The resident said he didn't witness the shooting but heard a "pop, pop, pop" shortly after he spoke to the man. At that stage the shopper was on one of the higher levels of the centre and looked down to see police standing over the man.
He said the shooting happened next to the fountain in the middle of the shopping centre precinct.
"For that to happen in Hornsby is just surreal," he said.
David Henry, who captured a dramatic image of the injured knifeman lying on the ground, was inside the shopping centre when he heard the shots.
"I immediately saw people running. There were a lot of mums with babies, yelling and panicked," he told news.com.au.
"I initially thought something had collapsed so I ran to the window above the fountain (inside the shopping centre) and saw a police woman holding her gun over the suspect.
"As I got there (the man on the ground) was not very well. He was prostrate ... he was looking around gingerly. There was a lot of blood on the ground."
Mr Henry, a professional photographer, pulled out his camera and started taking pictures.
"Within 20-30 seconds of hearing the shots, police were rendering assistance to two people. (The suspect) was on the ground being treated for his wounds, too."
Mr Henry said he is used to taking photographs at weddings but instinctively pulled out his camera when he saw what was taking place.
Police sources said the man was ranting.
Seven News journalist Robert Ovadia said the knifeman shouted "Allahu Akhbar" before police shot him, and that he had a history of mental health issues.
Sarah Henry, who arrived at the scene five minutes after the shooting, told the Daily Telegraph: "I saw police over bodies, it looked like three people were on the ground and police and paramedics were working on them.
"You could see the blood on the ground, on the pavement. My husband saw the aftermath, saw people running away from the area.. He called me and said, 'a shooting has happened.'
"There were a lot of people standing around watching, it's happened in the market area outside St George Bank."
Helen Wong, from the nearby Pho Ngon Restaurant, said she could see bodies and blood on the ground and that police had cordoned off the area.
Silvia Philip, who had a bakery stall at the markets, said the shooting was terrifying. "I've got a young assistant here and I just said 'get down, stay here'," Ms Philip told AAP.
"Within minutes police pulled up and three officers, two men and one woman, just ran up there towards the clock tower.
"The first thing I heard was the shots ... it was very disturbing, terrifying."
