A man who lethally injected his partner with heroin did not specifically measure the drug after the couple had earlier thrown out a lifesaving overdose antidote, a court has heard.
New details about the tragic and preventable death of Laura Crncevic were revealed in the ACT Supreme Court on Thursday.
Prosecutor Skye Jerome said Ms Crncevic's partner of seven years made a number careless and ultimately fatal mistakes on August 19, 2021.
Christopher Roy Weaver, 40, has pleaded guilty to charges of manslaughter and administering a declare substance after a long-running investigation led to his arrest last year.
The victim's sister told the court last month the offender had "exposed [Ms Crncevic] to a lifestyle of heavy drug use" when "he should have protected her and kept her safe".
As well as the pair having thrown out Narcan, an opioid overdose drug, and Weaver allegedly failing to measure the lethal shot, Ms Jerome said the man was himself affected by the drug when injecting his partner.
She said he had also noticed residue on the spoon after the injection and he should have realised there was an increased risk of death from the dose in question.
The court has previously heard Ms Crncevic struggled with a long history of complicated health.
"He agreed to inject her with a larger dose than normal despite knowing her poor health conditions," the prosecutor said on Thursday.
Defence barrister James Sabharwal described his client as the victim's "partial carer" and the case as a tragedy.
Ms Jerome had earlier asked the court to factor the overwhelmingly strong prosecution case into whether Weaver deserved the highest possible discount for his guilty plea.
Mr Sabharwal said without the man's admission, police would not have known he injected Ms Crncevic.
"It's only overwhelming because of his admissions," Justice Belinda Baker said.
The barrister responded: "I go further. But for his admission, that it was he who injected her, there's no case."
A clinical psychiatrist who assessed Weaver for a pre-sentence report said the man may have suffered from a number of mental illnesses at the time of the crime.
"However, in his opinion, there is no causal connection between the mental illness that the offender may have suffered at the time of the offence and the commission of the offence itself," the prosecutor said.
When Weaver entered his guilty pleas in October last year, appearing nonchalant about doing so, he told the court: "That's just what happens when you're a heroin addict.
"It was all an accident but yeah, guilty."
Justice Baker reserved her decision until a later date.
"This is a very difficult sentencing exercise and a very tragic case," she said.
