Blowhole murder: Killer uncle Derek Barrett's 'psychopathic' and 'sadistic' behaviour

9NEWS reporter Kelly Fedor watched as Derek Barrett was handed a 46-year sentence for the murder of his niece, Mengmei Leng: 

His voice broke, he put his head down and raised a tissue to his eyes, but there was nothing genuine about Derek Barrett's behaviour in a Sydney courtroom.

As if this was a performance, the 29-year-old declared his actions were for the grieving family – the same people who he had destroyed when he stabbed his niece, MengMei Leng, 40 times in their Campsie unit.

"I came here to tell the truth, I came here to help in some little way, some little way, whether they appreciate it or not," Barrett said.

When his motives were questioned, Barrett's voice rose, indignant at the suggestion.

"You think I would not trade places…I don't care about myself," he said.

Barrett had been secretly filming his 25-year-old niece in the bathroom and as she slept.

Then, last year, when Ms Leng arrived home, he tied her up, gagged her on her bed and then photographed her.

At some point over the next two days he stabbed her, threw her body in the boot of his car, drove to the Central Coast and tossed her into a blowhole.

They are events that should be seared into the brain, but the killer claims they are nothing more than flashes in his memory because he had taken ice a day or two beforehand.

He didn't flinch as he used his victim's name again and again.

"I made a promise to Mengmei that I wouldn't let it happen again," he said.

"I don't want to go near any kind of drug ever again, not if it means putting others at risk."

I've been reporting on courts for close to a decade and Barrett strikes me as a psychopath, one of the few I have encountered.

His crime wasn't the result of a drunken night out, some bad life choices or a childhood of abuse.

To me he ranks alongside Vincent Stanford, the school cleaner who raped and murdered Leeton teacher Stephanie Scott a week before her wedding.

The Macquarie Dictionary defines psychopathy as a personality "outwardly normal but characterised by a diminished sense of social responsibility, inability to establish deep human relationships, and sometimes, a tendency to manipulate others, and a lack of remorse for the harm done to others".

The respected forensic psychiatrist Dr Richard Furst said Barrett's IQ, concentration and memory were within normal limits.

He also didn't believe Barrett's claims of memory loss and said the number of stab wounds was indicative of a sadistic drive.

In sentencing Justice Helen Wilson went even further.

"It was a depraved and sadistic act committed by a man in a position of trust to Ms Leng," she said.

"He had the air in the witness box of someone playing a part and saying what he thought someone should say to present the best possible impression of himself.

"Whilst he was occasionally tearful his distress seemed somewhat contrived."

As the judge detailed Barrett's sexual perversion in front of packed courtroom, he stared at the floor.

He was no longer enjoying the attention and it was very clear he hadn't fooled anyone.

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