A Sydney drug boss and her associate have been jailed for 40 years over the "brutal and callous" murders of a drug cook and his girlfriend in 2013.

Key points: Both Dung Thi Ngo and Kevin Ly received a non-parole period of 30 years

Both Dung Thi Ngo and Kevin Ly received a non-parole period of 30 years Justice Geoffrew Bellew described the killings as "brutal and callous"

Justice Geoffrew Bellew described the killings as "brutal and callous" However, Justice Bellew said the murders were not a contract killing

Drug "queenpin" Dung Thi Ngo, 44, and her associate Kevin Ly, 27, were found guilty by a jury in November.

Ngo suspected cook Son Thanh Nguyen, 39, had stolen ice from a lab operating from the garage of a Canley Vale home.

Mr Nguyen and his girlfriend Thi Kim Lien Do, 35, were confronted by Ngo, Ly and several unidentified men at the property in April 2013.

According to witnesses, Ly strangled Mr Nguyen to death with a rope, but there was no evidence of how Ms Do died.

The bodies of the victims were discovered bound with cable ties and wrapped in bedding at separate locations in south west Sydney nine months apart.

Supreme Court Justice Geoffrey Bellew said the "brutal and callous" nature of Mr Nguyen's death was laid bare during a post-mortem examination which revealed extensive injuries.

He sentenced both offenders to 40 years in prison with a non-parole period of 30 years.

Justice Bellew said there was no evidence Ms Do played any role in the drug manufacturing.

The court heard Ms Do, who was tied up in a bedroom of the home, pleaded "don't kill me, I do not know anything" before she died.

"She was murdered because both Ngo and Ly were fearful that if she remained alive, she would be in a position to alert authorities to the circumstances around Mr Nguyen's death," Justice Bellew said.

According to two unidentified witnesses, as Mr Nguyen was being strangled by Ly, Ngo demanded: "Give it back, do you want to give it back or not?"

Both witnesses received indemnity in return for their evidence and one claimed to have seen Ngo hand over a box containing "a stack of $50 notes" prior to the deaths.

But Justice Bellew said he wasn't able to accept the Crown's submission that the murders constituted a contract killing.

He said the two key witnesses both appeared at times unreliable, with some material contradictions to evidence they gave police.

Ngo and Ly will be eligible for early release in 2046.