'Worrying signs.' The sociopathic tendencies that defined the Bourke St killer from childhood.

On January 20, 2017, James Gargasoulas screeched his way through the CBD of Melbourne.

He drove as fast as he could, driving into every person he saw.

He was calm.

He was expressionless.

He even had a cigarette in his mouth.

He looked to passersby like he was merely out on his Sunday drive.

But he wasn’t.

He was mowing down pedestrians and killing them – he murdered six innocent victims including a three-month-old baby and a 10-year-old girl.

27 others were injured.

Watch a snippet of the Four Corners investigation here. Post continues after video.

But for Gargasoulas, this act of mass murder was not his first crime. He had an extensive rap sheet, a history of drug abuse, and known mental instability.

In the years since the Bourke Street attack, the question remains: why was he still on the streets?

Most of the evidence used in the case against Gargasoulas hasn’t been seen by the public before, but last night Four Corners gave us an insight into the man behind the horrific crime.

Gargasoulas was brought up with his younger brother, Angelo, by their single father in the small South Australian town of Coober Pedy.

"It was one massive trauma," Angelo Gargasoulas told Four Corners when asked to describe their childhood.

He and his brother were belted and bashed up by their father too many times to count.

A belt, a branch, a metal bar - even having their heads smashed together -their father's rage was unrelenting.

The boy's mother lived in Melbourne and would come to visit on occasion, but she would only last a few days before retreating back to the city.

From a young age, Gargasoulas showed sociopathic tendencies and his brother noted his behaviour ramped up when he started smoking weed with his mates and stealing his dad's car to go and do donuts outside of town.

He also used to get picked on a lot at school because he was different, a bit crazy and eccentric.

Aged 14, Gargasoulas smuggled explosives into school to get revenge on the kids making fun of him.

The school was shut down, but no one was injured.

In his 20s, Gargasoulas was a regular ice user and was dealing drugs in his hometown.

Local Johnboy Jelcic remembers a disturbing conversation with Gargasoulas, in which he asked if he would ever kill someone.

“I said no, why would you ask me that… He said he’d have no problem harming someone even fatally so if it needed to happen,” Mr Jelcic told Four Corners.

With men Gargasoulas wasn't aggressive, but with women he was extremely violent.

“I’ve seen him drop a woman onto the floor, drag her by the hair, knock a woman unconscious, completely," his brother described.

In 2016, the year before he committed mass murder, he deliberately crashed his car into his girlfriend's car, because he thought she was cheating on him.

She spent 23 days in hospital with spinal injuries.

At the end of that year, he moved to Melbourne and by this stage his rap sheet was apparently "20 pages long," and included everything from driving while disqualified, reckless conduct causing affray, assaulting police and escaping custody.

While there, he again accused his now pregnant girlfriend of cheating. She told police he was punching her with both fists.

Three weeks later, he kidnapped his brother's friend.

Angelo had warned police it wasn't just people his brother knew that were in danger - it was everyone.

Before Christmas 2016, he picked up a sex worker and told her he had a gun. No action was taken by police after she reported the incident.

Six days before Bourke Street, he was arrested.

He laughed during the interview as his charges were listed.

Gargasoulas was bailed. Victoria is the only state that uses bail volunteers to hear cases, and the person that saw Gargasoulas was a teacher who let him off despite police opposing it.

In the days before Bourke Street, Gargasoulas told a priest the "world was going to end in a month's time," attacked his mother's partner with a burning bible and stole his commodore - the car he would use to kill six people in Bourke Street.

In the depths of a drug induced psychosis, he called police repeatedly threatening them, swearing, and telling them about the world's end.

The morning of Bourke Street, Gargasoulas stabbed his brother and left him fighting for life.

It was the fourth time in nine hours police had been called for James Gargasoulas, but he fled the scene.

"I think James Gargasoulas and subsequent incidents like that Bourke Street tragedy are the inevitable result of 20 years of pushing decision from the geographical location of the incident that's occurring, in front of people who are witnessing it, all the way up to someone else in an office miles away from where it's happening, " Greg Davies, a former Police Association boss told Four Corners.

An hour before Gargasoulas committed mass murder, he told a senior police officer in a text message "I've calculated my options. I either die in jail or die trying to run from the boys..."

They exchanged 33 messages in the lead up to Bourke Street, but he soon stopped replying to the officer's fervent pleas to stop.

In just 55 seconds, he hit a total of 33 people before being tasered and then shot by police.

In February, he was sentenced to life in prison, and later this year a coronial inquest will look into exactly what police knew about Gargasoulas and why he was out on bail.

How was a man with a rap sheet as long as Gargasoulas not already sitting in a prison cell?