A Chinese woman who stabbed her ex-lover's wife and grandson to death with garden shears started taking ice when she began to suspect the man wasn't going to marry her, a court has heard.
Crown prosecutors say Cai Xia Liao murdered Mai Mach and her grandson Alistair Kwong, 4, because she wanted Mai's husband, Brian Mach, to help her become an Australian citizen.
But defence barrister David Gibson disputes that Liao, 45, was only after citizenship.
Liao, who wailed and wept throughout her court hearing on Wednesday, went to the Machs' home in March while Mrs Mach was at work, drugged and bound Mr Mach and then stabbed Alistair to death with garden shears.
Liao later killed Mrs Mach when she got home from work, after nine hours of waiting in a "sustained rage".
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Liao told Mr Mach: "I cut the bitch's throat ... I have killed everyone to make you suffer", prosecutor Mark Rochford said.
She had previously offered to pay Mr Mach to marry her so she could live in Australia with her daughter.
Mr Gibson said Mr Mach had promised marriage, and Liao turned to drugs when she began to suspect it wouldn't happen.
She was desperately unhappy, Mr Gibson told Liao's pre-sentence hearing in the Victorian Supreme Court on Wednesday.
"It was a very strong relationship, in which Miss Liao put great hope."
Ice played no role in the killings, the court heard.
Liao wailed, rocked, covered her face and slumped against her translator throughout the hearing.
Mr Mach said he blames himself for what happened, and wants to die so he can be with his wife and grandson.
In a victim impact statement, Mr Mach said his daughters and their families will no longer speak to him.
"I'm so alone. My whole family has fallen apart."
Mr Mach and his wife were separated when Mr Mach met Liao in 2011, according to police documents.
The court heard Liao started threatening to kill Mrs Mach in November, several months before the double-murder.
In a series of messages, Liao told Mr Mach she was full of hatred and he was forcing her to act.
"What you're going to see will be most tragic, it's all because of you," she said.
Liao will be sentenced by Justice Lex Lasry on a date to be set.
* Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14
