Corey Loveridge, who killed a western Sydney teenager in an unprovoked attack, has been jailed for at least 30 years.

His co-offender AB, who cannot be named because he was a juvenile at the time of the crime, was also sentenced to a 30-year non-parole period for the murder of Alan "Ray Ray" Gordon who was brutally stabbed in December, 2010.

Loveridge, 21, was found guilty of murder by a jury last April.

AB pleaded guilty before the matter came to trial.

Their 17-year-old victim was stabbed multiple times at St Marys on December 2010 and died from massive blood loss.

Loveridge is a cousin of Kieran Loveridge, who killed teenager Thomas Kelly in an unprovoked attack at Kings Cross in July last year.

Kieran Loveridge will be sentenced next week.

Justice Michael Adams described the St Marys stabbing murder as an "appalling crime" and a "cowardly, sadistic and deadly attack".

Justice Adams said the pair got "unimaginable satisfaction or pleasure" from the murder.

"This makes them very dangerous individuals," he said.

The pair got a maximum jail period of 45 years but will be eligible for parole in December 2040.

When supporters of victims families began to clap, Justice Adams stopped them, saying it was "a sad matter" not a matter for rejoicing.

The pair's sentence also takes into account other offences including a break-and-enter on the night of the murder.

Alan's father Ronald Hussey told reporters outside the court that he hoped the pair wouldn't get out in his lifetime.

He described his son as an angel.

"He would do anything for anyone," Mr Hussey said.

"My son was doing the same thing he did for years, which was go down for his mother early in the morning to get her money out.

"Wrong place, wrong time.

"He just started working, he just loved his job, he just never got a chance.

"I no longer live at home... (his death) has pulled the family apart."