Brendan Neil subjected his girlfriend Simone Quinlan to a deadly beating in front of friends to punish her for "snitching", after she made a family violence report to police.

The mother of two was viciously kicked, punched and tormented at Neil's Melton home in Melbourne, in August 2015.

The killer and his friends all took ice, and Wayne Marmo sawed off the barrel of a point 22 rifle as the group watched Neil unleash the savage bashing.

Once it appeared Quinlan was dead or dying she was wrapped in a sheet and placed in the tray of Marmo's utility.

Wayne Marmo said to Brendan Neil "he's got to get rid of her, if she's snitched before imagine what she'd do now if he took her to hospital" Justice Jane Dixon recounted in sentencing.

Marmo was described as a "loyal friend" who fired five shots into Quinlan's head as she lay lifeless in the back of his ute.

The 26-year-old dumped Simone's body down a mineshaft in Kangaroo Flat and set it alight.

The judge was critical, telling Marmo: "You were prepared to involve yourself in a murder because of this loyalty."

Marmo washed and torched the vehicle, while Neil sanded his floorboards to remove any blood stains.

Neil contacted Quinlan's family to say the couple had split, in an attempt to avoid any suspicion over the 33-year-old's disappearance.

The court heard in the days leading up to the killing Neil had hit his girlfriend of four months over the head with a baseball bat.

He later convinced Quinlan to withdraw her family violence complaint with police.

Both Neil and Marmo were undergoing community corrections orders at the time of the murder and both men have a history of family violence offending.

Neil pleaded guilty to murder and was sentenced to 26 years behind bars, while Marmo was jailed for 24.

© Nine Digital Pty Ltd 2017