UPDATE 1:50pm: A 20-year-old man will spend at least 18 years behind bars for the "ferocious" and "unprovoked" murder of Dawesville teenager Jessie Cate.
Kyle Rohan Garth, of Pinjarra, was sentenced to a life jail term in the Supreme Court today, with a non-parole period of 18 years. This means Garth will still be aged in his 30s when he becomes eligible for release.
Details of how and why Garth murdered his ex-girlfriend's 15-year-old sister were revealed in court for the first time today, including how Garth strangled Jessie twice in his car - the second time with an intention to kill her to avoid being caught.
He told police he and Jessie were fighting in his car, after he picked her up from her part-time job at Woolworths in Falcon on December 12 last year, when within minutes he pulled the car over, lost his temper and lashed out.
Justice Jenkins said Garth had no real motive and this murder had not only devastated Jessie's family, but had also disturbed and impacted the wider community.
She told Garth he abused the trust Jessie and her family had in him in a "gross and awful way".
The judge described the attacks on Jessie as "ferocious", "unprovoked" and selfish.
Wearing prison greens, Garth spent his time in the dock mainly hunched over with his head bowed as Jessie's family saw him in person for the first time since he killed the high school student.
After strangling her, Garth, who had previously dated Jessie's older sister Emma for a couple of months, buried Jessie in a shallow grave in Bouvard.
In sentencing submissions today, prosecutor Carmel Barbagallo said Garth, a window tinter who used to work with the victim at Woolworths, offered to pick Jessie up from work telling her he had something to tell her alone. Those who overheard their conversation said the pair were smiling and it appeared their exchange was friendly.
Garth misled police for more than seven hours the next day when he concocted a story that he had dropped Jessie off at an oval to see friends.
Many inconsistencies were found in his story and Garth eventually confessed to murdering Jessie, saying they were arguing about his break-up with Emma, his current relationship and the fact he was no longer around as a male role model for Jessie's younger siblings when he pulled his car over and lost his temper. "I ended up suffocating her, I choked her with my hands, I don't know what came over me," he said.
When asked what was going through his mind when he was choking Jessie, Garth told detectives: "That's what disturbed me most - I was sorry and angry and that I love my partner, as that's all that was going through my head."
As he was blocking the road, another driver pulled up, prompting Garth to get out and speak to the other driver before driving off.
The court was told Garth then heard Jessie murmur and mumble and realised she was still alive.
Garth choked her with one hand whilst still driving - a position he held for more than 10km until he reached the site where he would bury her body.
Garth hid Jessie's body under logs and branches, returned home to Pinjarra to get a shovel and then went back to bury the teenager's body.
He told detectives he strangled her the second time out of fear of getting caught and when asked what his intention was at that time he replied: "kill her and I did".
The court was told Garth had spent a lot of time with Jessie's family while he was dating Emma and still remained on friendly terms with them after the break-up.
Jessie's family were in court today and saw Garth in person for the first time since he killed Jessie.
Ms Barbagallo said the impact of this senseless loss of life on Jessie's family and the wider Mandurah community was immeasurable.
Garth had no criminal record and no mention was made during sentencing submissions today of any major mental illness.
Defence lawyer Brian Mahon said his client wanted to apologise to everyone affected by his crime and he was fully aware that he shattered many lives that night.
He said his client bitterly regretted his actions and accepted he had a price to pay for ending Jessie's life. Mr Mahon said Garth conceded that during the second choking episode he intended to kill Jessie, but that the first attack was spontaneous with no planning.
"He's aware what he faces will only be a fraction of the suffering (that the Cate family will have to endure)," he said.
The murder of the popular teenager prompted a tidal wave of grief in the Mandurah community, but Mr Mahon said before this tragedy his client was also well-liked and respected in the community.
Garth had scratches on his face from Jessie during the first attack, but Ms Barbagallo said when Garth strangled her the second time "he effectively killed a girl who couldn't defend herself".
She said Garth had time to reevaluate his actions and choose a different path, but did not.
She said when Garth called Jessie's mother the morning after the murder, pretending not to know what had happened, it showed "callousness and coldness". Ms Barbagallo said Garth had also committed a breach of trust because Jessie and her family had no reason to think her life would be in danger in his company.
Justice Jenkins said while there was no pre-planning or weapon involved in this murder, it also involved a "terribly violent death" of a young person.
She said Garth still had the support of his mother, stepfather and his partner, who is 16 years his senior and who was his girlfriend at the time he murdered Jessie.
Outside court, Jessie's family welcomed the sentence, which was higher than they hoped, but showed Garth some compassion.
"It's more years that he's going to spend in prison than our gorgeous Jessie spent alive," Jessie's uncle Ric Troode said.
"Nothing is going to bring Jessie back, her memory will outlive Kyle's name forever and a day, she's never, ever going to be forgotten.
"I'm not going to be angry and say I hope he rots in hell ... I feel for him, he is a young man, we hope that he comes out of this a better person. They said that he had an unblemished character, that he was of good standing, but people of unblemished characters and good standing don't murder 15-year-olds ... there's no excuse."
Mr Troode said Garth's apology in court today provided them no solace.
Jessie's mother Judy Cate said outside court she and her family would never recover from her daughter's violent murder, saying they had lost the best thing they ever had.
"It happened so quickly, she didn't have a chance to defend herself or have a chance to get away, he took the intention to kill her without any thought towards Jessie herself and us as a family," she said.
"If he was remorseful, he should have let her live the first time."
Ms Cate said her daughter was "perfect" and "everything a parent could hope for in a child".