A 42-year-old Perth man has been jailed for life after admitting to undercover police he murdered a woman at his house and buried her body under his garage.

Keith Edward Earnshaw was sentenced in the Perth Supreme Court on Thursday to life imprisonment with a 23-year minimum for killing 40-year-old Helen Rocha in September 2013.

He had pleaded guilty to Ms Rocha's murder in July.

The court was told Earnshaw had lured Ms Rocha to his Parmelia home on the false premises of arranging a drug deal, before strangling her and burying her body in his garage.

Her remains were found in February this year after an elaborate undercover police operation was set up when detectives were unable to find any evidence linking him to the disappearance.

It was not until undercover operatives contacted Earnshaw under the pretence of offering him work that the nature of the crime emerged.

Prosecutor Amanda Forrester said when his role as a suspect was raised in a fake job interview, Earnshaw told the interviewer he had killed Ms Rocha and disposed of her body at his home.

The pretend employer then offered to find some men to help him move the body to another location.

When they arrived and Earnshaw's property, he revealed her burial location.

He was arrested the following day.

Earnshaw had earlier repeatedly denied any involvement in Ms Rocha's disappearance, the court heard.

Killer cut off victim's hair

During a police interview in February after his arrest, he admitted the crime, telling detectives he initially strangled her with his hands, before binding her hands, taping her mouth, and tying cable ties around her throat.

He then removed her jewellery and clothing and buried her under slabs in his garage.

Earnshaw also cut off Ms Rocha's hair and hid it in empty pot plants on his property.

The court heard he used the woman's mobile phone to send a text pretending to be her, saying she was going to Albany for a few days.

The 42-year-old was identified early in the investigation as a person of interest as he was the last person known to see Ms Rocha before she disappeared.

Police concerns were heightened when Earnshaw regularly changed his account of his movements on the day the mother-of-two disappeared.

Earnshaw offered no explanation or motive for the murder.

He told detectives he had been high on methamphetamine and was "looping out".

Earnshaw's defence told the court his client had consumed as much as 0.05 grams of meth on the day of the crime.

Justice Robert Mitchell said he had "struggled to see even a hint of remorse" while watching the recorded interviews of Earnshaw's confession.

He said the killer's reactions and emotions were those of a person who had realised "the game was up" and was more concerned with his own fate.

That assessment was backed up by Ms Forrester, who told the court Earnshaw had only admitted his guilt when "confronted with irrefutable evidence".

Outside the court Ms Rocha's sister Olimpia De Faria said she felt relieved at the length of Earnshaw's sentence.

"It doesn't matter how long he's in there for - the pain and the emptiness that we feel will never go away," she said.

"It's something that will be with us for the rest of our lives."

She said her sister's death was a "senseless act".

"He was high on drugs and felt like taking someone else's life," Ms De Faria said.