Wilson, 39, was on Tuesday sentenced to three years and six months’ imprisonment after pleading guilty to perverting the course of justice.

The sentence will be served concurrently with his 30 1/2 year jail term for murdering autistic Scarsdale teenager Timmy O'Brien in 2013 and two counts of incitement to murder.

Wilson, who was on remand for murder at the time, was charged with perverting the course of justice after he repeatedly asked his mother, Shirley Wilson, and brother, Eddie Wilson, to intimidate prosecution witnesses to change their statements against him at his trial. 

During his plea hearing in September, the court heard Wilson wrote regularly to his mother while in custody.

At one point he also tried to enlist the help of the Bandidos motorcycle club to terrorise the witnesses.

"... if you want me out for Christmas get then lien (sic) dog to tell the truth", Wilson wrote in one letter to his mother.

"You should be getting this down this is you [sic] job to make this happen mum ... get it done don't be scared."

In September The Age reported Wilson, who has a congenital intellectual disability, indicated he was aware police were recording and monitoring his conversations from remand.

Prosecutor Ray Gibson at the time told the court Wilson took the risk of getting caught because "he had a lot to gain and a lot to win".

The offending was serious and "strikes at the heart of the administration of justice", Mr Gibson said.

Wilson told his family on a phone call that some of the witnesses needed a "flogging" and that "...if she doesn't tell the truth she f---ing won't be around for the trial and I don't give a f--k whose listening."

Wilson's brother Eddie told him on the phone: "They [got] the fear of God put through them and they'll do what they're told to do.

"I've done my best today and they'll all be getting changed them statements otherwise they'll go back tomorrow and the next day and the next day and the next day," he said.

Wilson also tried to write to a member of the Bandidos motorcycle club asking for his help, but Corrections intercepted the letter before it was mailed out.

Judge Mark Taft said Wilson's crime was "extremely serious" and that he had engaged in a "concerted, repetitive and energetic campaign to interfere with witnesses."

During sentencing on Tuesday, Mr Taft said he believed there was a degree of overlap between this conduct and the conduct which resulted in Wilson imprisoned in 2014 for two counts of incitement to murder where he enlisted another remandee, a former police officer, to murder witnesses at a price of $80,000.

Mr Taft said the targets of both types of offending coincided, and could properly be described as a course of conduct over an extended period of time for the same purpose of preventing witnesses from giving evidence.

He said it was probable if Wilson was sentenced for the single charge of perverting the course of justice alongside the murder and incitement to murder charges in the Supreme Court, the total effective sentence would not have been significantly altered.

But for the plea of guilty, Wilson would have been sentenced to four years and six months jail, and had his 26 year non-parole period extended.

Wilson is due for parole in 2039.

- with The Age.