Ms Lyons, 47, and Mr Lyons, 45, are each charged with murder in relation to the death of 39-year-old Samantha Kelly in Kangaroo Flat about January 23 2016, as well as attempted murder.

Justice Stephen Kaye has started his final charge before the jury retires to consider the verdicts.

The prosecution argues the two accused plotted with former partner and housemate, Peter Arthur, to kill Ms Kelly so Ms Lyons could take custody of the deceased woman’s four young children, because she was desperate for children.

Arthur has admitted to killing Ms Kelly with a hammer in a unit at the Wesley Street property the four adults shared, and told the court during the trial he and the two accused had earlier tried to kill her by drug overdose.

On the charges of attempted murder, Crown prosecutor Fran Dalziel said the prosecution relied on the evidence of a toxicologist who said the drugs found in Ms Kelly’s body tissue and hair were over-the-counter medications or had been prescribed to Christine Lyons.

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Ms Dalziel said the evidence suggested there was no therapeutic reason to take these drugs together.

She said the prosecution also relied on Arthur’s evidence and that of the accused’s friend and relative, Shiralee Lyons, that there were conversations in which Ms Kelly’s murder was discussed, beginning prior to Christmas 2015. Ms Dalziel also raised Ms Lyons’ visit to the doctor and purchase of drugs on January 20, 2016.

Mr Lyons’ evidence in his police interview that Ms Kelly was not feeling well the week before she died pointed to the earlier attempt to kill her, she said.

The prosecution also relied on Arthur’s evidence that he and the two accused all participated in spiking drinks for Ms Kelly, Ms Dalziel said, with him having told the court Mr Lyons crushed up the tablets and at least once took tablets to Ms Kelly.

In relation to the charge of attempted murder, the jury heard they had to be convinced beyond reasonable doubt that the accused were party to an agreement, arrangement or understanding to kill Ms Kelly.

Ms Dalziel said the prosecution also needed to prove that the accused intended Ms Kelly to be killed, they acted in support of the agreement, and in accordance with this agreement, Ms Kelly was given medication with the intention of killing her.

The jury also needed to be satisfied that this act was sufficiently connected to the murder of Ms Kelly.

Ms Dalziel said motive was not an element of the offence, it informed the other evidence.

“Motive is very important in this case, there's no question and we've put it before you very strongly that the motive is for Christine to have the children and the two men supporting her in that goal,” she said.

In regards to the charge of murder, Ms Dalziel said the motive was a “powerful support” for Arthur’s version of events that on the night of the murder, Ms Lyons and Mr Lyons had said Ms Kelly needed to be killed, and Mr Lyons had instructed him to use a hammer.

She said the prosecution also relied on lies told by the defendants after the death, including that Ms Kelly had left in the middle of the night and had been using drugs.

There was a difference, Ms Dalziel asserted, in someone saying they did not know what had happened and making the claims about Ms Kelly that Ms Lyons and Mr Lyons had done.

“One of them is, ‘I don't know’. The other one is a story which blackens Samantha's name, it makes her an uncaring mother who abandons her children, and she's a drug user,” she told the jury.

She said the evidence that the two accused and Arthur had all told this story indicated they were all part of a plan to kill Ms Kelly and cover up her death.

The large number of people who said they heard this story from Ms Lyons, Ms Dalziel said, demonstrated her involvement in the plan to kill Ms Kelly.

She questioned Mr Lyons’ reasoning behind not telling police of the murder when he knew Arthur had killed Ms Kelly. “The only reasonable explanation for those lies and for moving the body is that he was involved in the agreement to kill Samantha and he did those things to cover up his own involvement and to hide his involvement in that agreement,” she said.

She said that while Mr Lyons told this story less often, he supported Ms Lyons’ telling of it.

The jury was told the prosecution also needed to prove four elements in relation to the separate charge of murder, one of which was that the accused were party to an agreement, arrangement or understanding to kill Ms Kelly, and remained party to that when she was killed.

The prosecution also had to prove they intended Ms Kelly be killed, acted in support of the agreement, and that Arthur did kill Ms Kelly as part of that agreement.

Ms Dalziel said the prosecution’s case was that Ms Lyons had said Ms Kelly had to be killed and encouraged that to happen, and Mr Lyons had also said she needed to be killed.

Arthur’s evidence that Mr Lyons also instructed him to use the hammer, she said, also showed Mr Lyons acted in support of the agreement.

On the final element, Ms Dalziel said the defence’s claim Arthur had acted in anger after Ms Kelly tried to hit him was not reasonable.

“It's a bizarre overreaction, on that version of events, it's a bizarre, extraordinary overreaction to a lethargic taking a bit of a swing at him and he just kills her,” she said.

Ms Dalziel urged the jury to not “cherry-pick” evidence and instead look at the evidence as a whole.

“They planned to kill her by killing her by drugs to make it look like a suicide and when that failed, the plan was changed and it was agreed she would be killed immediately and Peter killed her for that reason, and for that reason alone,” she said.

The defence lawyers for Christine Lyons and Ronald Lyons have contended that Peter Arthur, the man who has already admitted to killing Samantha Kelly in 2016, acted alone when he murdered the mother of four and not in a plot with the two defendants.

In his final address to the Supreme Court, Christine Lyons’ lawyer Peter Kilduff admitted that his client had lied about what happened to Ms Kelly following the murder.

But he said these lies did not make Ms Lyons guilty of murder or attempted murder, and invited the jury to instead convict her of assisting an offender, or being accessory after the fact.

Mr Kilduff suggested Ms Lyons lied because she was fearful of being implicated in the murder even through she was innocent, and wanted to protect Arthur.

He told the jury to consider what resources Ms Lyons had to do something about the murder, having no money and having found herself “trapped” in an environment with a man who had killed a woman.

Arthur was a violent man, he said, highlighting evidence that he had assaulted people and admissions he had hit one of the children in the household, and letters written in prison by Ms Lyons in which she said she was subject to threats and abuse from Arthur.

​Mr Kilduff argued that Arthur’s first version of the killing he gave in a police interview, that he murdered Ms Kelly in self-defence, was the true version as he did not have time to think once confronted with Ms Lyons’ claim that she believed him to be responsible. “He confesses fully. He doesn't lie or obfuscate,” he said.

The presence of drugs prescribed to Ms Lyons in Ms Kelly’s system was not enough proof the accused was part of a murder plot, he argued, saying she regularly attended the doctor and visited chemists.

He addressed evidence that Ms Lyons had called two of Ms Kelly’s children by different names, telling the jury that it was “not so far-fetched” that the two women discussed changing names to distance or antagonise the father of one of the children, with whom evidence showed Ms Kelly had a turbulent relationship.

Mr Kilduff sought to cast doubt on the evidence of witnesses called by the prosecution, including Ms Kelly’s cousin, who gave evidence she heard Ms Kelly being killed over the phone, but did not tell police until months later.

He argued that evidence Ms Kelly was drugged and isolated in her final days was inconsistent with evidence of her movements.

He said the conversations Shiralee Lyons gave evidence of – that she heard the murder being planned with the accused – did not happen, and drew attention to inconsistencies in her evidence and Arthur’s evidence about these conversations.

Mr Kilduff also spoke of lies Arthur had told during the investigation and in previous court appearances, including his change in story from killing Ms Kelly alone to being part of a plot.

“This case, we say, rests on the truthfulness reliability and credibility of Peter Arthur. A failure. He fails all of those tests,” Mr Kilduff said.

Mr Lyons’ defence lawyer, Jarrod Williams, also told the jury his defendant should be punished for assisting an offender for helping move Ms Kelly’s body, but likewise argued it did not make him guilty of murder or attempted murder.

He argued that the prosecution’s case against Mr Lyons rested on Arthur.

“Peter Arthur, a man whose oath means nothing to him. A perjurer,” Mr Williams said. “A man whose supposed memory of being directed to kill Samantha by Ronald, came to him in these flashbacks.”

Mr Williams told the jury that without Arthur, there was no evidence Mr Lyons crushed up medication to drug Ms Kelly, nor that he gave her any medications, or was party to any agreement to kill the victim.

He said Arthur was the only witness to give evidence Mr Lyons directed him to use a hammer to kill Ms Kelly, and the only witness to say he murdered her in accordance with an agreement with the two accused.

“If you have a reasonable doubt about the veracity of Peter Arthur's evidence linking Ronald Lyons to the charges of attempted murder and murder, the only verdict open to be returned on those charges is not guilty,” he said.

Mr Williams argued there was no evidence given that Mr Lyons had motive to kill Ms Kelly.

He also told the jury that aside from the evidence of Peter Arthur, its evidence in the case against Mr Lyons was circumstantial.

Mr Williams asked whether the evidence proved beyond reasonable doubt that Arthur did not act alone, saying he was the person who had control of Ms Lyons’ medications, it was him Shiralee Lyons said raised the idea of drugging Ms Kelly, and it was him who said Ms Kelly was sick after drinks one night.

“He's the one who brutally struck Samantha multiple times to the head. He was the one who disposed of Samantha's body… He's the one who created the story about Samantha having walked out,” he said.

The prosecution’s argument, Mr Williams said, that the toxicology evidence helped prove there was an agreement to try murder Ms Kelly, was flawed because this evidence was not inconsistent with Arthur acting alone.

He also posed the question as to whether conversations about killing Ms Kelly were, simply, conversations only.

Mr Williams told the jury Arthur was a “boorish, nasty thug”, easy to anger, who by his own admission had murdered a woman with a hammer.

He argued that Arthur’s evidence to the court was a lie given for his own benefit, drawing attention to inconsistencies in his various versions of events since the murder, including earlier assertions he killed Ms Kelly in self-defence and acted alone.

Mr Williams said the jury could not convict a man of murder or attempted murder based on Arthur’s evidence.

“He's lied repeatedly at every point in these proceedings. There's no reason why you should now think he's now telling the truth,” Mr Williams said.