'I knew at 10 he'd be a killer.' Ivan Milat wasn't a normal child. He had a 'different psyche'.

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At 10 years old, Ivan Milat had the mind of a killer.

According to his brother Boris, a longing to cause pain was simply “built into him”. It was a cruel streak that ran deep.

Born on December 27, 1944, in Guildford, New South Wales to Croatian emigrant Stjepan Marko “Steven” Milat, and Australian woman, Margaret Elizabeth Piddleston, Ivan was the fifth-born of their 14 children.

Speaking on Sunday Night, former police superintendent Clive Small – who was intimately involved with the investigation into the seven backpacker murders Ivan is convicted of – said the Milat children had far from an ordinary upbringing.

Watch the preview for the Ivan Milat episode of Channel 7’s Sunday Night. Post continues after video.

“The Milat family is quite an unusual family,” explains Clive. “Ivan’s father was a Croatian, lived on a small island just off Croatia. [He] wasn’t here that long before he met his wife who was quite young at the time, and they married a couple of years later. She started almost from the day they were married having children, two of whom died. He had 13 brothers and sisters.”

The book, Sins Of The Brother, written by Les Kennedy and Mark Whittaker, reveals that times for the family were incredibly tough.

The enormous family lived in cottages with dirt floors, sheds, and decrepit houses in rural areas of NSW.

Ivan’s father Stephen worked 10-hour shifts as a wharf labourer, arriving home late at night. The family also ran a market garden, which the children pitched in to help with.

But the means to properly care for them were never available.

Stephen's work, always gruelling, left him exhausted, grumpy, and at times violent.

Speaking to Steve Pennells on Sunday Night, Boris Milat recalls loud and vicious arguments between his mother and his father, who was a heavy drinker. Given their living situation – having once lived together in a large shed during one of their many moves across NSW – there was never an escape from the yelling and physical assault his mother endured.

Boris recalled his mother Margaret being struck "at least once a week" by his father.

But when it came to disciplining the children, Margaret had a fiery temper of her own.

She hit Boris once with a knife, and while he can't remember what for, the scars remain visible.

"Nearly cut me bloody arm off," he said.

On another occasion, he was hit so hard with a tomato stake it broke his arm.

Not only were the Milat children exposed to violence in their home lives, they grew up with knives and guns as toys, and were encouraged to play shooting games in the backyard.

This was normal, everyday life for a young Ivan Milat, whose life as a career criminal – paving the way for a reputation as Australia's most notorious serial killer – began early.

While many of the 10 Milat boys were well known to local police during their upbringing, Ivan displayed antisocial behaviour at a young age, leading to a stint in a residential school at age 13.

According to his brother Boris, Ivan's horrific killing spree of seven backpackers came as no surprise.

"He was going to kill somebody from the age of 10. It was built into him. He had a different psyche. He’s a psychopath, and it just manifested itself with, 'I can do anything, I can do anything,'" he said.

"I knew he was on a one-way trip. I knew that it was just a matter of how long."

Ivan, now 74 – who is dying of stomach and oesophagus cancer – has been in prison for his crimes since 1996, but has never admitted to the crimes he was convicted of.

He is likely to die without ever admitting guilt to the families of Caroline Clarke, 21, Joanne Walters, 22, James Gibson, 19, Deborah Everest, 19, Simone Schmidl, 21, Gabor Neugebauer, 21, and Anja Habschield, 20.

Boris, 76, a man who was given his first gun at age five, doesn't remember a time when he or his 13 siblings didn't have access to a gun.

But he believes that of the 14, his younger brother Ivan was wired to be a murderer.

"[Ivan] was pretty normal up until 12, 14," Boris recalled in the interview on Sunday Night. "I heard about it from his mates, you know. They’d all boast about [how] they’d go out at night and do things with machetes. I heard he cut a dog in half with a machete while he was growing up."

By his early teens, Ivan was already committed to a life of small-time crime, breaking into homes and stealing.

At 17, he was was in a juvenile detention centre for theft, and two years later, he was involved in a shop break in. The criminal behaviour continued – worsening as he grew older.

In 1964, he was sentenced to 18 months for a break and enter, and a month after release, he was arrested for driving a stolen car and sentenced to two years hard labour.

From here, his crimes became increasingly severe, his sentences longer. But he showed no signs of slowing down.

In September 1967, aged 23, he was sentenced to three years for theft. In April 1971, he was charged with the abduction of two 18-year-old hitchhikers. He had raped one of them.

While awaiting trial, he was involved in a string of robberies with some of his brothers, before faking his suicide and fleeing to New Zealand for a year.

He was arrested again in 1974, but the robbery and kidnap cases against him failed at trial. In 1975, he met a woman named Karen – who, then 16, was pregnant with his cousin's child. They married in 1983, but she left him in 1987 due to domestic violence. They divorced in October 1989.

His relationship with Karen wasn't the first woman close to the family he was involved with. Ivan has a 54-year-old daughter, Lynise, whose mother was Boris' wife. Ivan had been having an 11-year affair with her.

Boris told The West Australian in 2015 about how he took a rifle to Ivan’s home, with the intention of killing his younger brother when he found out the truth.

Boris, who was outcast from the Milat family for speaking to journalist Steve Pennells, also revealed Ivan had confessed his first experience of seriously injuring another person at 17.

He shared that he'd accidentally shot a taxi driver during a failed attempted robbery. His rifle had misfired and hit Neville Knight in the spine, leaving the young father paralysed from the waist down.

Ivan fled, leaving an innocent man placed with the blame. The wrongly-convicted man went on to serve five years for the shooting.

Fast forward to 1992 and 1993, when the remains of four women and three men – all backpackers – were discovered in the Belanglo State Forest.

Discovered in shallow graves, their partially buried bodies lay face-down in dense forest, with their hands positioned behind their backs.

"The bodies were left there on the basis he believed no one else would see them anyway," Clive Small explained of where the bodies were found.

Clive believes Ivan chose his victims – all in their late teens or early 20s, five of which were overseas travellers – because he thought their disappearance would go unnoticed.

"There would be very few people that would have seen them or could possibly have given him up. They were isolated from other members of their family, and that in effect would give the killer more protection and less likely chance of detection."

Caroline Clarke and Joanne Walters, from the UK were the first to be discovered. Joanne had been stabbed 21 times in the back and 14 in the chest. Caroline had been shot 10 times in the head.

Victorian couple Deborah Everist and James Gibson – the youngest of his victims – were next. James had been stabbed eight times. Deborah had been savagely beaten.

And the last to be found were German couple Anja Habschied and Gabor Neugebauer, not far from the remains of another German backpacker, Simone Schmidl.

Anja had been decapitated, and despite an extensive police search, her head has never been found.

Ivan Milat received seven life sentences for the murders and will die in Goulburn's Supermax prison.

But while there was never any evidence that any other family members – all of whom endured the same difficult upbringing – were involved in Ivan's crimes, his conviction put them under enormous pressure, especially when a judge voiced suspicions that Milat had not acted alone.

The burden of the family name, Boris says, has never left him.

You can watch Sunday Night's Ivan Milat special on 7plus.

For more on this topic:

• In 1982, Colin Powis hitched a ride with Ivan Milat. He was almost his first victim.
• "A story of unfathomable cruelty." The incriminating photograph found in Ivan Milat's home.
• At 20, Ivan Milat had an affair with his brother's wife. They had a daughter together.
• Ivan Milat could die within weeks. Here are 14 unsolved cases he's been linked to.
• 17 years after Ivan Milat's last murder, his nephew killed someone in Belanglo State Forest.