A 26-year-old British woman who was obsessed with serial killers and fantasised about a “screaming pleading victim” has been sentenced to life in prison – along with her Australian housemate – over the brutal “thrill killing” of an 18-year-old in Perth.

Jemma Lilley and Trudi Lenon, a 44-year-old mother of three and well-known “submissive” in the local bondage scene, showed no emotion as a court in Western Australia sentenced them for the “morally repugnant” murder of Aaron Pajich, whom they lured to their home, executed and buried under fresh concrete.

Justice Stephen Hall said the murder in 2016 was committed for the “pitiless pursuit of your own desires ... you killed for your own pleasure.”

The court heard that Lilley, who moved to Perth from Stamford, Lincolnshire, in 2010 and was working as a night manager in a supermarket, had been obsessed with murder for much of her life and once told a friend she wanted to kill someone before the age of 25.

Once she had ticked off murder from her "bucket list" she was so "full of herself and euphoric" that she could not help boasting to a work colleague, prosecutor James McTaggart told the court during a four-week trial last year.

She referred to herself as SOS, a serial killer character in a book called Play Zone, which she wrote as a teenager in Britain and published online. It was also the nickname of the “Son of Sam” serial killer, David Berkowitz, who murdered six people in New York in the 1970s.

Lilley claimed a list of torture methods found at her home was part of her research for future books.

Aaron Pajich, 18, was lured to his death

In 2012, Lilley married a gay man, who, she claimed, looked “identical” to the American serial killer John Wayne Gacy. After her husband's death in 2014, she began a lesbian relationship with his close friend, who introduced her to Lenon.

The pair quickly became close and Lilley, then aged 24, invited Lenon, who was struggling financially, to move into her home along with Lenon’s three children.

The pair called their home “Elm Street” after the A Nightmare on Elm Street horror film series; Lilley’s hero was Freddy Kruger, the main villain in the series.

Within a fortnight of living together, they began sending text messages describing their murder fantasies.

Lilley allegedly wrote: "I feel as though I cannot rest until the blood or flesh of a screaming victim is gushing out and pooling on the floor... I cannot shift this belief that the world has become not only ready for me but it needs me to be ready."

Lenon allegedly responded: "It is definitely time - I am ready, you are ready".

In the days before the murder, the pair went to hardware stores and bought a saw, cement, bleach, a drop sheet, a large barrel and 100 litres of hydrochloric acid.

On June 13 2016, the pair lured Mr Pajich to their home. Mr Pajich, who had autism, was a friend of Lenon’s 14-year-old son.

The court heard that Lilley attacked Mr Pajich from behind soon after he arrived and tried to strangle him with a garotte but it snapped. Lenon then held him down and Lilley allegedly stabbed him in the neck and chest.

The pair were arrested and charged soon after the murder. Lilley pleaded not guilty. Lenon claimed she was an accessory.

The pair were sentenced to a minimum of 28 years in jail.

After the sentence was delivered, Mr Pajich's step-mother Veronica Desmond said of Lilley and Lenon: "I hope you rot, I hope you live to regret what you've done."